[Bug 37052] WM_TRANSIENT_FOR occasionally contains unmapped windows

http://bugs.winehq.org/show_bug.cgi?id=37052

--- Comment #4 from Jasper St. Pierre  ---
Yes, the ICCCM never explicitly says that WM_TRANSIENT_FOR needs to be mapped.
What it *does* say, however, is that the WM should treat unmapped windows as
windows that don't exist from its point of view.

So from the point of view of the WM, an unmapped window in WM_TRANSIENT_FOR is
an invalid value, since it's effectively the same as a window that doesn't
exist.