I have added a polygon without nodes. To do it, hold "Return" button when you add a polygon.
Then click at "Add Nodes" button. Marble crashed.

Reproducible: Always

Steps to Reproduce:
1. Go to "Edit Maps" panel. (Settings->Panels->Edit Maps)
2. Add a polygon without nodes. Hold "Return" button at your keyboard to close "Add Polygon" dialog.
3. Click "Add Nodes" button.

Actual Results:  
Marble crashed.


Backtrace:
#0  0x00007ffff57acd27 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007ffff57ae418 in __GI_abort () at abort.c:89
#2  0x00007ffff7967c22 in qt_message_output (msgType=msgType@entry=QtFatalMsg, buf=0x1639b88 "ASSERT: \"!isEmpty()\" in file /usr/include/qt4/QtCore/qvector.h, line 263")
    at global/qglobal.cpp:2386
#3  0x00007ffff7967f89 in qt_message(QtMsgType, const char *, typedef __va_list_tag __va_list_tag *) (msgType=msgType@entry=QtFatalMsg, 
    msg=msg@entry=0x7ffff7ad38c0 "ASSERT: \"%s\" in file %s, line %d", ap=ap@entry=0x7fffffffb8e8) at global/qglobal.cpp:2432
#4  0x00007ffff7968794 in qFatal (msg=msg@entry=0x7ffff7ad38c0 "ASSERT: \"%s\" in file %s, line %d") at global/qglobal.cpp:2615
#5  0x00007ffff79687d6 in qt_assert (assertion=assertion@entry=0x7ffff6861b64 "!isEmpty()", file=file@entry=0x7ffff6861990 "/usr/include/qt4/QtCore/qvector.h", 
    line=<optimized out>) at global/qglobal.cpp:2060
#6  0x00007ffff659e44c in last (this=0x1495cf0) at /usr/include/qt4/QtCore/qvector.h:263
#7  Marble::GeoDataLineString::last (this=<optimized out>) at /home/sergobot/marble/sources/src/lib/marble/geodata/data/GeoDataLineString.cpp:185
#8  0x00007fffdd471346 in Marble::AreaAnnotation::updateRegions (this=0x113a240, painter=0x7fffffffbfb0)
    at /home/sergobot/marble/sources/src/plugins/render/annotate/AreaAnnotation.cpp:628
#9  0x00007fffdd46e17c in Marble::AreaAnnotation::paint (this=0x113a240, painter=0x7fffffffbfb0, viewport=0x7ee280)
    at /home/sergobot/marble/sources/src/plugins/render/annotate/AreaAnnotation.cpp:71
#10 0x00007fffdd45e1f2 in Marble::AnnotatePlugin::render (this=0x935c00, painter=0x7fffffffbfb0, viewport=0x7ee280, renderPos=..., layer=0x0)
    at /home/sergobot/marble/sources/src/plugins/render/annotate/AnnotatePlugin.cpp:223
#11 0x00007ffff670e8f6 in Marble::LayerManager::renderLayers (this=0x7ee290, painter=painter@entry=0x7fffffffbfb0, viewport=0x7ee280)
    at /home/sergobot/marble/sources/src/lib/marble/LayerManager.cpp:174
#12 0x00007ffff6678b8b in Marble::MarbleMap::paint (this=0x7de248, painter=..., dirtyRect=...) at /home/sergobot/marble/sources/src/lib/marble/MarbleMap.cpp:769
#13 0x00007ffff66608f2 in Marble::MarbleWidget::paintEvent (this=0x7de5f0, evt=<optimized out>) at /home/sergobot/marble/sources/src/lib/marble/MarbleWidget.cpp:733
#14 0x00007ffff6e4ece8 in QWidget::event (this=0x6330, event=0x6330) at kernel/qwidget.cpp:8775
#15 0x00007ffff6dff11c in QApplicationPrivate::notify_helper (this=this@entry=0x6c0170, receiver=receiver@entry=0x7de5f0, e=e@entry=0x7fffffffc370) at kernel/qapplication.cpp:4570
#16 0x00007ffff6e05870 in QApplication::notify (this=0x7fffffffdb80, receiver=0x7de5f0, e=0x7fffffffc370) at kernel/qapplication.cpp:4356
#17 0x00007ffff7a7286d in QCoreApplication::notifyInternal (this=0x7fffffffdb80, receiver=receiver@entry=0x7de5f0, event=event@entry=0x7fffffffc370)
    at kernel/qcoreapplication.cpp:953
#18 0x00007ffff6e497ad in sendSpontaneousEvent (event=0x7fffffffc370, receiver=0x7de5f0) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:234
#19 QWidgetPrivate::drawWidget (this=this@entry=0x7d6350, pdev=0xf4df50, rgn=..., offset=..., flags=68, flags@entry=-15264, sharedPainter=sharedPainter@entry=0x0, 
    backingStore=0xf07540) at kernel/qwidget.cpp:5599
#20 0x00007ffff7011088 in QWidgetBackingStore::sync (this=0xf07540) at painting/qbackingstore.cpp:1365
#21 0x00007ffff6e3ea70 in QWidgetPrivate::syncBackingStore (this=0x7346b0) at kernel/qwidget.cpp:1894
#22 0x00007ffff6e4ef00 in QWidget::event (this=0x6330, this@entry=0x734490, event=0x6330, event@entry=0x7fffffffca60) at kernel/qwidget.cpp:8693
#23 0x00007ffff72116f3 in QMainWindow::event (this=0x734490, event=0x7fffffffca60) at widgets/qmainwindow.cpp:1478
#24 0x00007ffff6dff11c in QApplicationPrivate::notify_helper (this=this@entry=0x6c0170, receiver=receiver@entry=0x734490, e=e@entry=0x7fffffffca60) at kernel/qapplication.cpp:4570
#25 0x00007ffff6e05870 in QApplication::notify (this=0x7fffffffdb80, receiver=0x734490, e=0x7fffffffca60) at kernel/qapplication.cpp:4356
#26 0x00007ffff7a7286d in QCoreApplication::notifyInternal (this=0x7fffffffdb80, receiver=receiver@entry=0x734490, event=event@entry=0x7fffffffca60)
    at kernel/qcoreapplication.cpp:953
#27 0x00007ffff7012b1e in sendEvent (event=0x7fffffffca60, receiver=0x734490) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:231
#28 sendUpdateRequest (updateImmediately=true, widget=0x734490) at painting/qbackingstore.cpp:534
#29 QWidgetBackingStore::markDirty (this=0xf07540, rect=..., widget=widget@entry=0x13f84c0, updateImmediately=updateImmediately@entry=true, 
    invalidateBuffer=invalidateBuffer@entry=false) at painting/qbackingstore.cpp:722
#30 0x00007ffff6e3f0a5 in QWidget::repaint (this=0x13f84c0, rect=...) at kernel/qwidget.cpp:10497
#31 0x00007ffff6e3f0e3 in QWidget::repaint (this=this@entry=0x13f84c0) at kernel/qwidget.cpp:10447
#32 0x00007ffff71b9dbd in QAbstractButtonPrivate::click (this=this@entry=0x13f84f0) at widgets/qabstractbutton.cpp:536
#33 0x00007ffff71b9ed4 in QAbstractButton::mouseReleaseEvent (this=0x13f84c0, e=0x7fffffffcf50) at widgets/qabstractbutton.cpp:1123
#34 0x00007ffff727132a in QToolButton::mouseReleaseEvent (this=<optimized out>, e=<optimized out>) at widgets/qtoolbutton.cpp:723
#35 0x00007ffff6e4ece8 in QWidget::event (this=0x6330, event=0x6330) at kernel/qwidget.cpp:8775
#36 0x00007ffff6dff11c in QApplicationPrivate::notify_helper (this=this@entry=0x6c0170, receiver=receiver@entry=0x13f84c0, e=e@entry=0x7fffffffcf50) at kernel/qapplication.cpp:4570
#37 0x00007ffff6e059be in QApplication::notify (this=<optimized out>, receiver=0x13f84c0, e=0x7fffffffcf50) at kernel/qapplication.cpp:4113
#38 0x00007ffff7a7286d in QCoreApplication::notifyInternal (this=0x7fffffffdb80, receiver=receiver@entry=0x13f84c0, event=event@entry=0x7fffffffcf50)
    at kernel/qcoreapplication.cpp:953
#39 0x00007ffff6e0507f in sendEvent (event=<optimized out>, receiver=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:231
#40 QApplicationPrivate::sendMouseEvent (receiver=receiver@entry=0x13f84c0, event=event@entry=0x7fffffffcf50, alienWidget=alienWidget@entry=0x13f84c0, 
    nativeWidget=nativeWidget@entry=0x734490, buttonDown=buttonDown@entry=0x7ffff78f3578 <qt_button_down>, lastMouseReceiver=..., spontaneous=true) at kernel/qapplication.cpp:3178
#41 0x00007ffff6e7abde in QETWidget::translateMouseEvent (this=this@entry=0x734490, event=event@entry=0x7fffffffd2b0) at kernel/qapplication_x11.cpp:4634
#42 0x00007ffff6e7a477 in QApplication::x11ProcessEvent (this=0x7fffffffdb80, event=event@entry=0x7fffffffd2b0) at kernel/qapplication_x11.cpp:3627
#43 0x00007ffff6ea2432 in x11EventSourceDispatch (s=0x6bca90, callback=0x0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:146
#44 0x00007ffff4e75c5d in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#45 0x00007ffff4e75f48 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#46 0x00007ffff4e75ffc in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#47 0x00007ffff7aa0031 in QEventDispatcherGlib::processEvents (this=0x6bc3c0, flags=...) at kernel/qeventdispatcher_glib.cpp:434
#48 0x00007ffff6ea24e6 in QGuiEventDispatcherGlib::processEvents (this=<optimized out>, flags=...) at kernel/qguieventdispatcher_glib.cpp:204
#49 0x00007ffff7a714f1 in QEventLoop::processEvents (this=this@entry=0x7fffffffd690, flags=...) at kernel/qeventloop.cpp:149
#50 0x00007ffff7a71805 in QEventLoop::exec (this=this@entry=0x7fffffffd690, flags=...) at kernel/qeventloop.cpp:204
#51 0x00007ffff7a76f67 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1225
#52 0x0000000000425949 in main (argc=2, argv=0x7fffffffdd38) at /home/sergobot/marble/sources/src/apps/marble-qt/qtmain.cpp:258