st/nine: Handle Window Occlusion

st/nine: Handle Window Occlusion

Apps can know if the window is occluded by checking for
specific error messages. The behaviour is different
for Device9 and Device9Ex.

This allow games to release the mouse and stop rendering
until the focus is restored.

In case of multiple swapchain we do care only of the device one.

Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Axel Davy <axel.davy@ens.fr>