SUMMARY
When trying to reply to one particular email, kmail crashes. It only happens with this email, which I can't attach for privacy reasons (it has one doc attachment and one pdf attachment). With both Qt 5.13.2 and 5.14.0

#0  0x00007ffff59913ec in TemplateParser::TemplateParserJob::processWithTemplate (this=this@entry=0x55555a424bf0, tmpl=...)
    at /usr/include/qt/QtCore/qsharedpointer_impl.h:312
#1  0x00007ffff5993136 in TemplateParser::TemplateParserJob::process (this=this@entry=0x55555a424bf0, aorig_msg=..., afolder=503)
    at /usr/src/debug/messagelib-19.12.0/templateparser/src/templateparserjob.cpp:202
#2  0x00007ffff5afc8a1 in MessageComposer::MessageFactoryReplyJob::start (this=this@entry=0x55555a518800)
    at /usr/src/debug/messagelib-19.12.0/messagecomposer/src/helper/messagefactoryreplyjob.cpp:50
#3  0x00007ffff5af76dc in MessageComposer::MessageFactoryNG::createReplyAsync (this=0x55555a3c3230)
    at /usr/src/debug/messagelib-19.12.0/messagecomposer/src/helper/messagefactoryng.cpp:306
#4  0x00007ffff7de2023 in ?? () from /usr/lib/libkmailprivate.so.5
#5  0x00007ffff7d731e5 in ?? () from /usr/lib/libkmailprivate.so.5
#6  0x00007ffff7d708bb in ?? () from /usr/lib/libkmailprivate.so.5
#7  0x00007ffff6b0f33e in ?? () from /usr/lib/libQt5Core.so.5
#8  0x00007ffff7d34faf in ?? () from /usr/lib/libkmailprivate.so.5
#9  0x00007ffff7d75d56 in ?? () from /usr/lib/libkmailprivate.so.5
#10 0x00007ffff6b0f33e in ?? () from /usr/lib/libQt5Core.so.5
#11 0x00007ffff7afca4d in KJob::result(KJob*, KJob::QPrivateSignal) () from /usr/lib/libKF5CoreAddons.so.5
#12 0x00007ffff7afd53c in KJob::finishJob(bool) () from /usr/lib/libKF5CoreAddons.so.5
#13 0x00007ffff6b0713a in QObject::event(QEvent*) () from /usr/lib/libQt5Core.so.5
#14 0x00007ffff7570472 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#15 0x00007ffff7579c89 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#16 0x00007ffff6ad9832 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#17 0x00007ffff6adc096 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQt5Core.so.5
#18 0x00007ffff6b32674 in ?? () from /usr/lib/libQt5Core.so.5
#19 0x00007ffff339f39e in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#20 0x00007ffff33a11b1 in ?? () from /usr/lib/libglib-2.0.so.0
#21 0x00007ffff33a11f1 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#22 0x00007ffff6b31cc0 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#23 0x00007ffff6ad839c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#24 0x00007ffff6ae03a6 in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#25 0x0000555555558064 in ?? ()
#26 0x00007ffff64ab153 in __libc_start_main () from /usr/lib/libc.so.6
#27 0x000055555555821e in ?? ()