Windows QPA: Clear maximized state before setting the normal geometry.

A sequence of state changes fullscreen, maximized and back can leave the
window in a maximized state after setting the top level style. It needs to
be cleared before applying the normal geometry, otherwise, the window ends
up with a maximized button and normal geometry. Amends change
e3288f24

.

Task-number: QTBUG-49709
Change-Id: I0bb4ac1d60693e25d5ee74e763d293405636bb13
Reviewed-by: Błażej Szczygieł <spaz16@wp.pl>
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>