window-actor: Update shape at construction time

When we attach an existing surface actor, the allocation may not
change, so we need to ensure that the shape region and geometry is
valid...

src/compositor/meta-window-actor.c

@@ -420,6 +420,7 @@ meta_window_actor_constructed (GObject *object)
                           "allocation-changed",
                           G_CALLBACK (surface_allocation_changed_notify),
                           self);
+      meta_window_actor_update_shape (self);
 
       g_signal_connect_object (window, "notify::decorated",
                                G_CALLBACK (window_decorated_notify), self, 0);