If you force-show a widget (e.g. `w.setVisible(True)`) before parenting it,
a small window will flash (appear and disappear) for a fraction of second,
which is a bit irritating.
If an attacker has access to the process' memory, it's probably already game over,
still we can make their life a bit harder.
I really tried but failed to encapsulate this logic inside PasswordLineEdit.
The destroyed signal arrives too late.
deleteLater is not called.
__del__ gets called too late.
