Fix a potential use-after-free

Author: mortie

main.c

@@ -102,6 +102,8 @@ static void destroy_surface(struct swaylock_surface *surface) {
 	}
 	destroy_buffer(&surface->buffers[0]);
 	destroy_buffer(&surface->buffers[1]);
+	destroy_buffer(&surface->indicator_buffers[0]);
+	destroy_buffer(&surface->indicator_buffers[1]);
 	wl_output_destroy(surface->output);
 	free(surface);
 }