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>

gdk/wayland/gdkdisplay-wayland.c

@@ -729,6 +729,8 @@ gdk_wayland_display_finalize (GObject *object)
 
   g_ptr_array_free (display_wayland->monitors, TRUE);
 
+  wl_display_disconnect(display_wayland->wl_display);
+
   G_OBJECT_CLASS (gdk_wayland_display_parent_class)->finalize (object);
 }