The Spice Gtk widget relies on pointer grabs to receive all pointer
events even after the pointer has left the window.

While that works on X11, on Wayland there is no active pointer grab,
so once the pointer has left the SPICE widget on Wayland, the events
are routed to the window with the pointer focus instead of ours.

To avoid the problem, on Wayland, we simply ungrab the pointer once it
leaves the window.

Thanks-to: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
#83


Acked-by: Victor Toso <victortoso@redhat.com>