user32: Use top level window as dialog parent for modal dialogs.

[Jacek Caban]

Hi Dmitry,

I will ask you one more time to go back to the code and being technical
instead of personal. Take a look at the code and show me a code path,
that makes enabling or disabling any different than before the patch. If
you can't then you will understand that the change is unrelated. If you
do, I'm happy to write a test for that case.

Jacek