Destroy thread windows also on process exit

[Dmitry Timoshkov]

"Alexandre Julliard" <julliard at winehq.org> wrote:

> I don't see how that would make a difference since we don't send
> messages to an exiting thread anywyay. Do you have a case where this
> is needed, or is it just a theoretical concern?

The bug was spotted by metafile test, and this patch fixes the issue
as well if you comment out a newly added DestroyWindow in metafile.c.

-- 
Dmitry.