avoid crash on closing

(gdb) bt
#0  0x00007fb258932c24 in QPlainTextEdit::clear() () from /usr/lib/libQt5Widgets.so.5
#1  0x00007fb25a29d4c0 in DiffEditor::clearData (this=0x5556bda20670) at /home/pister/local_ssd/devel/kde/src/kate/apps/lib/diff/diffeditor.h:70
#2  0x00007fb25a293294 in DiffWidget::clearData (this=0x5556bd989b10) at /home/pister/local_ssd/devel/kde/src/kate/apps/lib/diff/diffwidget.cpp:418
#3  0x00007fb25a2998dc in operator() (es=QProcess::CrashExit, exitCode=9, __closure=0x5556be1dc130) at /home/pister/local_ssd/devel/kde/src/kate/apps/lib/diff/diffwidget.cpp:398
#4  QtPrivate::FunctorCall<QtPrivate::IndexesList<0, 1>, QtPrivate::List<int, QProcess::ExitStatus>, void, DiffWidget::runGitDiff()::<lambda(int, QProcess::ExitStatus)> >::call (arg=<optimized out>, f=...)
at /usr/include/qt/QtCore/qobjectdefs_impl.h:146
#5  QtPrivate::Functor<DiffWidget::runGitDiff()::<lambda(int, QProcess::ExitStatus)>, 2>::call<QtPrivate::List<int, QProcess::ExitStatus>, void> (arg=<optimized out>, f=...) at /usr/include/qt/QtCore/qobjectdefs_impl.h:256
#6  QtPrivate::QFunctorSlotObject<DiffWidget::runGitDiff()::<lambda(int, QProcess::ExitStatus)>, 2, QtPrivate::List<int, QProcess::ExitStatus>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void **, bool *) (
which=<optimized out>, this_=0x5556be1dc120, r=<optimized out>, a=<optimized out>, ret=<optimized out>) at /usr/include/qt/QtCore/qobjectdefs_impl.h:443
#7  0x00007fb257abe931 in QtPrivate::QSlotObjectBase::call (a=<optimized out>, r=<optimized out>, this=<optimized out>, this=<optimized out>, r=<optimized out>, a=<optimized out>)
at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#8  doActivate<false> (sender=0x5556be1d2430, signal_index=11, argv=0x7fff0da1ff90) at kernel/qobject.cpp:3923
#9  0x00007fb257a184bd in QProcess::finished (this=<optimized out>, _t1=<optimized out>, _t2=<optimized out>) at .moc/moc_qprocess.cpp:339
#10 0x00007fb257a14cc2 in QProcessPrivate::_q_processDied (this=0x5556be173950) at io/qprocess.cpp:1184
#11 0x00007fb257a19895 in QProcessPrivate::waitForFinished (msecs=30000, this=0x5556be173950) at io/qprocess_unix.cpp:878
#12 QProcess::waitForFinished (this=<optimized out>, msecs=30000) at io/qprocess.cpp:1930
#13 0x00007fb257a17236 in QProcess::~QProcess (this=<optimized out>, this=<optimized out>) at io/qprocess.cpp:1266
#14 0x00007fb257a1729e in QProcess::~QProcess (this=<optimized out>, this=<optimized out>) at io/qprocess.cpp:1273
#15 0x00007fb257ab4a65 in QObjectPrivate::deleteChildren (this=0x5556bdfa11e0) at kernel/qobject.cpp:2137
#16 0x00007fb25879be15 in QWidget::~QWidget() () from /usr/lib/libQt5Widgets.so.5
#17 0x00007fb25a1fa4ee in DiffWidget::~DiffWidget (this=0x5556bd989b10, __in_chrg=<optimized out>)
at /local/ssd/pister/devel/kde/build/kate/apps/lib/kateprivate_autogen/DTTFLNF7MJ/../../../../../../../../../../../home/pister/local_ssd/devel/kde/src/kate/apps/lib/diff/diffwidget.h:33
#18 DiffWidget::~DiffWidget (this=0x5556bd989b10, __in_chrg=<optimized out>)
at /local/ssd/pister/devel/kde/build/kate/apps/lib/kateprivate_autogen/DTTFLNF7MJ/../../../../../../../../../../../home/pister/local_ssd/devel/kde/src/kate/apps/lib/diff/diffwidget.h:33
#19 0x00007fb257ab189a in QObject::event (this=0x5556bd989b10, e=0x5556be1dd540) at kernel/qobject.cpp:1334
#20 0x00007fb258778b5c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#21 0x00007fb257a8de08 in QCoreApplication::notifyInternal2 (receiver=0x5556bd989b10, event=0x5556be1dd540) at kernel/qcoreapplication.cpp:1064
#22 0x00007fb257a8e913 in QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x5556bc46b720) at kernel/qcoreapplication.cpp:1821
#23 0x00007fb257ad4d48 in postEventSourceDispatch (s=0x5556bc5b31d0) at kernel/qeventdispatcher_glib.cpp:277
#24 0x00007fb255e6d87b in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#25 0x00007fb255ec4c89 in ?? () from /usr/lib/libglib-2.0.so.0
#26 0x00007fb255e6c132 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#27 0x00007fb257ad8b2c in QEventDispatcherGlib::processEvents (this=0x5556bc5b4e70, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#28 0x00007fb257a865ac in QEventLoop::exec (this=0x7fff0da20640, flags=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:69
#29 0x00007fb257a910d9 in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#30 0x00005556bb082eb1 in main (argc=<optimized out>, argv=<optimized out>) at /home/pister/local_ssd/devel/kde/src/kate/apps/kate/main.cpp:643