westoy: Schedule a full resize when we add a subsurface

If a client adds a subsurface, we need to make sure it's allocated
properly, so queue a resize and redraw on the parent window.

clients/window.c

@@ -4671,6 +4671,9 @@ window_add_subsurface(struct window *window, void *data,
 		assert(!"bad enum subsurface_mode");
 	}
 
+	window->resize_needed = 1;
+	window_schedule_redraw(window);
+
 	return widget;
 }