Fix resource leak in gdk_display_close() under Wayland
When using the gdk_display_close(), the handle to the Wayland compositor was not released. This could cause the consumption of all available handles, preventing other processes from accessing the display.
Fixing this by calling wl_display_disconnect() when releasing the GdkWaylandDisplay object.
Signed-off-by: Julien Ropé jrope@redhat.com