wlr_compositor: Move buffer damage clear to end of commit

It makes sense to do it here because it is where we null the buffer. The
buffer damage is only useful to us as long as we have the buffer.

types/wlr_compositor.c

@@ -564,6 +564,8 @@ static void surface_commit_state(struct wlr_surface *surface,
 	// released immediately on commit when they are uploaded to the GPU.
 	wlr_buffer_unlock(surface->current.buffer);
 	surface->current.buffer = NULL;
+
+	pixman_region32_clear(&surface->buffer_damage);
 }
 
 static void surface_handle_commit(struct wl_client *client,