clients: destroy wl_registry on exit

Plug an insignificant memory leak in demo programs that bother to clean
up at all.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/clients/window.c b/clients/window.c
index 20d09d5..c7767ae 100644
--- a/clients/window.c
+++ b/clients/window.c
@@ -4314,6 +4314,7 @@
 		wl_data_device_manager_destroy(display->data_device_manager);
 
 	wl_compositor_destroy(display->compositor);
+	wl_registry_destroy(display->registry);
 
 	close(display->epoll_fd);