Fix crash when doing open recent

Summary:

6212== Invalid read of size 8

6212== at 0x6B0FFB0: QUrl::QUrl(QUrl const&) (in /usr/lib/libQt5Core.so.5.13.0)

6212== by 0x53461BB: KRecentFilesAction::addUrl(QUrl const&, QString const&) (krecentfilesaction.cpp:159)

6212== by 0x1B53C7: kpMainWindow::addRecentURL(QUrl const&) (kpMainWindow_File.cpp:221)

6212== by 0x1B5BC3: kpMainWindow::open(QUrl const&, bool) (kpMainWindow_File.cpp:426)

6212== by 0x1B629D: kpMainWindow::slotOpenRecent(QUrl const&) (kpMainWindow_File.cpp:507)

6212== by 0x1BBEAA: QtPrivate::FunctorCall<QtPrivate::IndexesList<0>, QtPrivate::List<QUrl const&>, void, void (kpMainWindow::*)(QUrl const&)>::call(void (kpMainWindow::*)(QUrl const&), kpMainWindow*, void**) (qobjectdefs_impl.h:152)

6212== by 0x1BBA10: void QtPrivate::FunctionPointer<void (kpMainWindow::*)(QUrl const&)>::call<QtPrivate::List<QUrl const&>, void>(void (kpMainWindow::*)(QUrl const&), kpMainWindow*, void**) (qobjectdefs_impl.h:185)

6212== by 0x1BB717: QtPrivate::QSlotObject<void (kpMainWindow::*)(QUrl const&), QtPrivate::List<QUrl const&>, void>::impl(int, QtPrivate::QSlotObjectBase*, QObject*, void**, bool*) (qobjectdefs_impl.h:414)

6212== by 0x6BEEB6F: QMetaObject::activate(QObject*, int, int, void**) (in /usr/lib/libQt5Core.so.5.13.0)

6212== by 0x5347959: KRecentFilesAction::urlSelected(QUrl const&) (moc_krecentfilesaction.cpp:210)

6212== by 0x5345B08: KRecentFilesActionPrivate::_k_urlSelected(QAction*) (krecentfilesaction.cpp:98)

6212== by 0x53475B7: KRecentFilesAction::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) (moc_krecentfilesaction.cpp:96)

6212== Address 0x10be2b50 is 32 bytes inside a block of size 40 free'd

6212== at 0x48399AB: free (vg_replace_malloc.c:530)

6212== by 0x6A5D3D7: QMapDataBase::freeNodeAndRebalance(QMapNodeBase*) (in /usr/lib/libQt5Core.so.5.13.0)

6212== by 0x5348F66: QMapData<QAction*, QUrl>::deleteNode(QMapNode<QAction*, QUrl>*) (qmap.h:280)

6212== by 0x5348453: QMap<QAction*, QUrl>::remove(QAction* const&) (qmap.h:948)

6212== by 0x5346786: KRecentFilesAction::removeAction(QAction*) (krecentfilesaction.cpp:219)

6212== by 0x54F1DA9: KSelectAction::clear() (in /usr/lib/libKF5WidgetsAddons.so.5.61.0)

6212== by 0x534693B: KRecentFilesAction::clearEntries() (krecentfilesaction.cpp:249)

6212== by 0x5346AB8: KRecentFilesAction::loadEntries(KConfigGroup const&) (krecentfilesaction.cpp:261)

6212== by 0x1B538D: kpMainWindow::addRecentURL(QUrl const&) (kpMainWindow_File.cpp:216)

6212== by 0x1B5BC3: kpMainWindow::open(QUrl const&, bool) (kpMainWindow_File.cpp:426)

6212== by 0x1B629D: kpMainWindow::slotOpenRecent(QUrl const&) (kpMainWindow_File.cpp:507)

6212== by 0x1BBEAA: QtPrivate::FunctorCall<QtPrivate::IndexesList<0>, QtPrivate::List<QUrl const&>, void, void (kpMainWindow::*)(QUrl const&)>::call(void (kpMainWindow::*)(QUrl const&), kpMainWindow*, void**) (qobjectdefs_impl.h:152)

6212== Block was alloc'd at

6212== at 0x483877F: malloc (vg_replace_malloc.c:299)

6212== by 0x6A5D798: QMapDataBase::createNode(int, int, QMapNodeBase*, bool) (in /usr/lib/libQt5Core.so.5.13.0)

6212== by 0x5348E0D: QMapData<QAction*, QUrl>::createNode(QAction* const&, QUrl const&, QMapNode<QAction*, QUrl>*, bool) (qmap.h:225)

6212== by 0x5348362: QMap<QAction*, QUrl>::insert(QAction* const&, QUrl const&) (qmap.h:726)

6212== by 0x5346707: KRecentFilesAction::addAction(QAction*, QUrl const&, QString const&) (krecentfilesaction.cpp:210)

6212== by 0x5346F26: KRecentFilesAction::loadEntries(KConfigGroup const&) (krecentfilesaction.cpp:307)

6212== by 0x1B48BF: kpMainWindow::setupFileMenuActions() (kpMainWindow_File.cpp:99)

6212== by 0x1ACA61: kpMainWindow::setupActions() (kpMainWindow.cpp:505)

6212== by 0x1ABD19: kpMainWindow::init() (kpMainWindow.cpp:218)

6212== by 0x1AB253: kpMainWindow::kpMainWindow() (kpMainWindow.cpp:67)

6212== by 0x196C6F: main (kolourpaint.cpp:118)

Subscribers: tcanabrava

Differential Revision: https://phabricator.kde.org/D23329