wayland: Don't ignore wl_keyboard.leave if surface is gone

keyboard_handle_leave() might be called with a NULL surface resource
(for example if the surface was destroyed after the event was sent). If
so, we should still deal with the keyboard focus lost event, otherwise
we will both leak (the keyboard_focus GdkWindow reference) and miss
stopping the key repeat timer.

https://bugzilla.gnome.org/show_bug.cgi?id=755927

gdk/wayland/gdkdevice-wayland.c

@@ -1191,15 +1191,14 @@ keyboard_handle_leave (void               *data,
   GdkEvent *event;
   GdkWaylandDisplay *display = GDK_WAYLAND_DISPLAY (device->display);
 
-  if (!surface)
-    return;
-
-  if (!GDK_IS_WINDOW (wl_surface_get_user_data (surface)))
-    return;
-
   if (!device->keyboard_focus)
     return;
 
+  /* gdk_window_is_destroyed() might already return TRUE for
+   * device->keyboard_focus here, which would happen if we destroyed the
+   * window before loosing keyboard focus.
+   */
+
   stop_key_repeat (device);
 
   _gdk_wayland_display_update_serial (display, serial);