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.
diff --git a/clients/window.c b/clients/window.c
index 75e6418..a75a7f8 100644
--- a/clients/window.c
+++ b/clients/window.c
@@ -4671,6 +4671,9 @@
 		assert(!"bad enum subsurface_mode");
 	}
 
+	window->resize_needed = 1;
+	window_schedule_redraw(window);
+
 	return widget;
 }