SUMMARY
Whe using the filter bar and quickly typing while thumbnails are still being generated for the view (I think) Dolphin crashes

STEPS TO REPRODUCE
1. Open a folder with lots of folders with thumbnails (e.g. my KDE source folder which has lots of repos who all have a lovely GitLab icon these days)
2. Open filter bar (Ctrl+I)
3. Start filtering for a specific folder, I used "info" (for kinfocenter)

OBSERVED RESULT
Dolphin crashes

EXPECTED RESULT
Dolphin doesn't crash

SOFTWARE/OS VERSIONS
Dolphin: 20.11.70 git master as of a few days ago

Backtrace:
Thread 1 (Thread 0x7fc84899f800 (LWP 112841)):
[KCrash Handler]
#4  KItemListWidget::index (this=this@entry=0x0) at ./src/kitemviews/kitemlistwidget.cpp:72
#5  0x00007fc84f33b4d7 in KItemListView::setWidgetIndex (this=0x55e5be98dad0, widget=0x0, index=<optimized out>) at ./src/kitemviews/kitemlistview.cpp:1982
#6  0x00007fc84f3407f5 in KItemListView::slotItemsRemoved (this=0x55e5be98dad0, itemRanges=...) at ./src/kitemviews/kitemlistview.cpp:1202
#7  0x00007fc84d23f5ae in QtPrivate::QSlotObjectBase::call (a=0x7ffc0e85e680, r=0x55e5be98dad0, this=0x55e5be848100) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#8  doActivate<false> (sender=0x55e5be2cf390, signal_index=4, argv=0x7ffc0e85e680) at kernel/qobject.cpp:3886
#9  0x00007fc84d238977 in QMetaObject::activate (sender=<optimized out>, m=m@entry=0x7fc84f3d6c60 <KItemModelBase::staticMetaObject>, local_signal_index=local_signal_index@entry=1, argv=argv@entry=0x7ffc0e85e680) at kernel/qobject.cpp:3946
#10 0x00007fc84f2fd4c9 in KItemModelBase::itemsRemoved (this=<optimized out>, _t1=...) at ./obj-x86_64-linux-gnu/src/dolphinprivate_autogen/Z3MQH7AOBD/moc_kitemmodelbase.cpp:253
#11 0x00007fc84f31b032 in KFileItemModel::applyFilters (this=this@entry=0x55e5be2cf390) at ./src/kitemviews/kfileitemmodel.cpp:704
#12 0x00007fc84f31bb5e in KFileItemModel::setNameFilter (this=0x55e5be2cf390, nameFilter=...) at ./src/kitemviews/kfileitemmodel.cpp:658
#13 0x00007fc84f36e57d in DolphinView::setNameFilter (this=<optimized out>, nameFilter=...) at ./src/views/dolphinview.cpp:484
#14 0x00007fc84f6334d8 in DolphinViewContainer::setNameFilter (this=0x55e5be689e70, nameFilter=...) at ./src/dolphinviewcontainer.cpp:667
#15 0x00007fc84d23f5ae in QtPrivate::QSlotObjectBase::call (a=0x7ffc0e85e890, r=0x55e5be689e70, this=0x55e5be72af50) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#16 doActivate<false> (sender=0x55e5be6f1a90, signal_index=7, argv=0x7ffc0e85e890) at kernel/qobject.cpp:3886
#17 0x00007fc84d238977 in QMetaObject::activate (sender=<optimized out>, m=m@entry=0x7fc84f6cd000 <FilterBar::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7ffc0e85e890) at kernel/qobject.cpp:3946
#18 0x00007fc84f678b06 in FilterBar::filterChanged (this=<optimized out>, _t1=...) at ./obj-x86_64-linux-gnu/src/dolphinstatic_autogen/A7DZ2KMSNA/moc_filterbar.cpp:174
#19 0x00007fc84d23f5ae in QtPrivate::QSlotObjectBase::call (a=0x7ffc0e85e9a0, r=0x55e5be6f1a90, this=0x55e5be9a4cc0) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#20 doActivate<false> (sender=0x55e5be9d5e20, signal_index=7, argv=0x7ffc0e85e9a0) at kernel/qobject.cpp:3886
#21 0x00007fc84d238977 in QMetaObject::activate (sender=<optimized out>, m=m@entry=0x7fc84e339080 <QLineEdit::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7ffc0e85e9a0) at kernel/qobject.cpp:3946
#22 0x00007fc84df688a6 in QLineEdit::textChanged (this=<optimized out>, _t1=...) at .moc/moc_qlineedit.cpp:447
#23 0x00007fc84df6f20b in QLineEdit::qt_static_metacall (_o=0x55e5be9d5e20, _c=<optimized out>, _id=<optimized out>, _a=0x7ffc0e85eb10) at .moc/moc_qlineedit.cpp:255
#24 0x00007fc84d23f5e0 in doActivate<false> (sender=0x55e5be6904c0, signal_index=6, argv=0x7ffc0e85eb10) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:395
#25 0x00007fc84d238977 in QMetaObject::activate (sender=sender@entry=0x55e5be6904c0, m=m@entry=0x7fc84e339140 <QWidgetLineControl::staticMetaObject>, local_signal_index=local_signal_index@entry=3, argv=argv@entry=0x7ffc0e85eb10) at kernel/qobject.cpp:3946
#26 0x00007fc84df6fdb9 in QWidgetLineControl::textChanged (this=this@entry=0x55e5be6904c0, _t1=...) at .moc/moc_qwidgetlinecontrol_p.cpp:273
#27 0x00007fc84df736ed in QWidgetLineControl::finishChange (this=0x55e5be6904c0, validateFromState=<optimized out>, update=<optimized out>, edited=<optimized out>) at widgets/qwidgetlinecontrol.cpp:736
#28 0x00007fc84df764a3 in QWidgetLineControl::processKeyEvent (this=0x55e5be6904c0, event=event@entry=0x7ffc0e85f270) at ../../include/QtCore/../../src/corelib/tools/qrefcount.h:60
#29 0x00007fc84df689af in QLineEdit::keyPressEvent (this=0x55e5be9d5e20, event=0x7ffc0e85f270) at widgets/qlineedit.cpp:1794
#30 0x00007fc84de61275 in QWidget::event (this=this@entry=0x55e5be9d5e20, event=event@entry=0x7ffc0e85f270) at kernel/qwidget.cpp:8686
#31 0x00007fc84df6ea62 in QLineEdit::event (this=0x55e5be9d5e20, e=0x7ffc0e85f270) at widgets/qlineedit.cpp:1531
#32 0x00007fc84de1dcc3 in QApplicationPrivate::notify_helper (this=this@entry=0x55e5bdfcd050, receiver=receiver@entry=0x55e5be9d5e20, e=e@entry=0x7ffc0e85f270) at kernel/qapplication.cpp:3671
#33 0x00007fc84de273a6 in QApplication::notify (this=<optimized out>, receiver=0x55e5be9d5e20, e=0x7ffc0e85f270) at kernel/qapplication.cpp:3033
#34 0x00007fc84d2086aa in QCoreApplication::notifyInternal2 (receiver=0x55e5be9d5e20, event=0x7ffc0e85f270) at ../../include/QtCore/5.15.0/QtCore/private/../../../../../src/corelib/thread/qthread_p.h:325
#35 0x00007fc84de7f506 in QWidgetWindow::event (event=0x7ffc0e85f270, this=0x55e5be2c4ef0) at kernel/qwidgetwindow.cpp:288
#36 QWidgetWindow::event (this=0x55e5be2c4ef0, event=0x7ffc0e85f270) at kernel/qwidgetwindow.cpp:238
#37 0x00007fc84de1dcc3 in QApplicationPrivate::notify_helper (this=this@entry=0x55e5bdfcd050, receiver=receiver@entry=0x55e5be2c4ef0, e=e@entry=0x7ffc0e85f270) at kernel/qapplication.cpp:3671
#38 0x00007fc84de26c70 in QApplication::notify (this=0x7ffc0e85f6a0, receiver=0x55e5be2c4ef0, e=0x7ffc0e85f270) at kernel/qapplication.cpp:3417
#39 0x00007fc84d2086aa in QCoreApplication::notifyInternal2 (receiver=0x55e5be2c4ef0, event=0x7ffc0e85f270) at ../../include/QtCore/5.15.0/QtCore/private/../../../../../src/corelib/thread/qthread_p.h:325
#40 0x00007fc84d7103eb in QGuiApplicationPrivate::processKeyEvent (e=e@entry=0x55e5bf4f10b0) at kernel/qguiapplication.cpp:2346
#41 0x00007fc84d71559b in QGuiApplicationPrivate::processWindowSystemEvent (e=e@entry=0x55e5bf4f10b0) at kernel/qguiapplication.cpp:1952
#42 0x00007fc84d6ed2cb in QWindowSystemInterface::sendWindowSystemEvents (flags=flags@entry=...) at kernel/qwindowsysteminterface.cpp:1175
#43 0x00007fc84852e99e in xcbSourceDispatch (source=<optimized out>) at qxcbeventdispatcher.cpp:105
#44 0x00007fc84afeffbd in g_main_context_dispatch () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#45 0x00007fc84aff0240 in ?? () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#46 0x00007fc84aff02e3 in g_main_context_iteration () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#47 0x00007fc84d262e92 in QEventDispatcherGlib::processEvents (this=0x55e5be0a99c0, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#48 0x00007fc84d2071bb in QEventLoop::exec (this=this@entry=0x7ffc0e85f570, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:141
#49 0x00007fc84d20f354 in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#50 0x00007fc84d707d10 in QGuiApplication::exec () at kernel/qguiapplication.cpp:1867
#51 0x00007fc84de1dc39 in QApplication::exec () at kernel/qapplication.cpp:2811
#52 0x00007fc84f61d3cd in kdemain (argc=<optimized out>, argv=<optimized out>) at ./src/main.cpp:204
#53 0x00007fc84f4030b3 in __libc_start_main (main=0x55e5bc3fe060 <main>, argc=1, argv=0x7ffc0e85f848, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffc0e85f838) at ../csu/libc-start.c:308
#54 0x000055e5bc3fe09e in _start ()