Calling setHidden() in the widgets destructor causes an application crash

If QWidget::setHidden(bool hidden) is called in the widgets destructor the application crashes. The problem is that in src/gui/kernel/qapplication.cpp in function void QApplicationPrivate::sendSyntheticEnterLeave(QWidget *widget), the widgetUnderCursor is the widget that was being deleted.

The patch that fixes this bug is attached to this bugreport.