This can't be done properly without support from the native windowing
system.  However, it's a good bet to try the next window in the z-order
if it's the owner of the original window and it's in the same thread.
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>