[REG 5.9->5.10] Changing the tab order can cause an assert on exit

[REG 5.9->5.10] Changing the tab order can cause an assert on exit due to the fact that when it is deleting a widget then it tries to confirm that the focus chain is what it should be (in that focusPrev of the next points to the widget being deleted) and this is not the case at this point

In this case it happened when the tab order was explicitly changed with a QCheckBox, QTabWidget and a QTextEdit.