stage: Do not update when destroying a stage

During the stage destruction we should just skip event processing, since
we cannot guarantee that the stage is actually valid.

clutter/clutter-stage.c

@@ -815,6 +815,9 @@ _clutter_stage_do_update (ClutterStage *stage)
 
   priv = stage->priv;
 
+  if (CLUTTER_ACTOR_IN_DESTRUCTION (stage))
+    return FALSE;
+
   /* NB: We need to ensure we have an up to date layout *before* we
    * check or clear the pending redraws flag since a relayout may
    * queue a redraw.