user32: fix for the ending of menu tracking in the default handler of WM_CANCELMODE message.

[Rein Klazes]

Reece Dunn schreef:
> There is a checklist that Alexandre uses to judge patches before he
> accepts them. I can't remember the link to this, though.
>
> - Reece
>
>   
I can not remember this checklist, I would be interested if you find it.

And I think the delay has to do with the nature of this patch: until now 
the window handling does not know too much about the menu internals. It 
might take some convincing that this it necessary or Alexandre may have 
other ideas how to do that.

Rein.