Crash in QIconModeViewBase::itemsRect() when overriding QListView::startDrag()

The attached testcase crashes with Qt6 but not with Qt5 even I don't understand why. The fix is trivial but I'm not sure if we should allow to override startDrag() in QListView and if the QVector behavior in Qt5 is correct. Even valgrind does not print anything about this strange access:

void killMe(const QVector<QModelIndex> &indexes)
{
        qDebug() << indexes.capacity() << *indexes.begin();
}
...

killMe({})

The original report comes from https://www.qtcentre.org/threads/71383-Qt6-StartDrag-making-crash-on-Qt6