Application crashes when scanning a jpeg file with funky exif metadata.
When MetaEngine::Private::convertCommentValue() gets called for exif comment encoded using "Jis" charset and comment contains "\000\000..." (empty string) whole application segfaults.

Am using arch linux with:
extra/digikam 5.4.0-2
extra/qt5-base 5.8.0-5
extra/exiv2 0.25-3
extra/libkexiv2 16.12.2-1

Have also tried rebuilding digikam from git (master commit 1546044e48) and it crashes with same stacktrace, below is stack trace and patch that avoided the crash.


Thread 4 "Digikam::ScanCo" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffab5ef700 (LWP 20074)]
0x00007ffff427c3be in QTextCodec::toUnicode(char const*) const () from /usr/lib/libQt5Core.so.5
(gdb) bt
#0  0x00007ffff427c3be in QTextCodec::toUnicode(char const*) const () at /usr/lib/libQt5Core.so.5
#1  0x00007ffff65f1309 in  () at /usr/lib/libdigikamcore.so.5.5.0
#2  0x00007ffff6609409 in Digikam::MetaEngine::getExifComment() const () at /usr/lib/libdigikamcore.so.5.5.0
#3  0x00007ffff663baaa in Digikam::DMetadata::getImageComments(Digikam::DMetadataSettingsContainer const&) const () at /usr/lib/libdigikamcore.so.5.5.0
#4  0x00007ffff3ccf6ac in Digikam::ImageScanner::scanImageComments() () at /usr/lib/libdigikamdatabase.so.5.5.0
#5  0x00007ffff3cd1076 in Digikam::ImageScanner::scanFile(Digikam::ImageScanner::ScanMode) () at /usr/lib/libdigikamdatabase.so.5.5.0
#6  0x00007ffff3bfa86c in Digikam::CollectionScanner::scanNewFile(QFileInfo const&, int) () at /usr/lib/libdigikamdatabase.so.5.5.0
#7  0x00007ffff3bfc446 in Digikam::CollectionScanner::scanAlbum(Digikam::CollectionLocation const&, QString const&) () at /usr/lib/libdigikamdatabase.so.5.5.0
#8  0x00007ffff3bfc376 in Digikam::CollectionScanner::scanAlbum(Digikam::CollectionLocation const&, QString const&) () at /usr/lib/libdigikamdatabase.so.5.5.0
#9  0x00007ffff3bfca79 in Digikam::CollectionScanner::scanAlbumRoot(Digikam::CollectionLocation const&) () at /usr/lib/libdigikamdatabase.so.5.5.0
#10 0x00007ffff3bfccbb in Digikam::CollectionScanner::completeScan() () at /usr/lib/libdigikamdatabase.so.5.5.0
#11 0x00007ffff740c345 in Digikam::ScanController::run() () at /usr/lib/libdigikamgui.so.5.5.0
#12 0x00007ffff40476d8 in  () at /usr/lib/libQt5Core.so.5
#13 0x00007fffedfaa454 in start_thread () at /usr/lib/libpthread.so.0
#14 0x00007ffff33457df in clone () at /usr/lib/libc.so.6



diff --git a/libs/dmetadata/metaengine_p.cpp b/libs/dmetadata/metaengine_p.cpp
index 2b44e06c21..1819c503ea 100644
--- a/libs/dmetadata/metaengine_p.cpp
+++ b/libs/dmetadata/metaengine_p.cpp
@@ -416,7 +416,8 @@ QString MetaEngine::Private::convertCommentValue(const Exiv2::Exifdatum& exifDat
                else if (charset == "\"Jis\"")
                {
                        QTextCodec* const codec = QTextCodec::codecForName("JIS7");
-                       return codec->toUnicode(comment.c_str());
+                       const char *tmp = comment.c_str();
+                       return *tmp ? codec->toUnicode(tmp) : QStringLiteral("");
                }
                else if (charset == "\"Ascii\"")
                {