DelegateModel can crash with retranslate()

Doesn't seem to crash with Qt 6, or perhaps it was just good luck.

Unfortunately I couldn't reduce the example further, but attached example crashes if retranslate() is called repeatedly. To do that, click the button at the top few times.

Qt 5 in debug build triggers an assert QList::at which is called by QQmlDelegateModelPrivate::itemsRemoved().