simple clients: flush before destroying wl_display

Flush our pending destroy requests to the server before destroying the
wl_display.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/clients/simple-shm.c b/clients/simple-shm.c
index 7d4f177..61771c9 100644
--- a/clients/simple-shm.c
+++ b/clients/simple-shm.c
@@ -235,6 +235,7 @@
 	if (display->compositor)
 		wl_compositor_destroy(display->compositor);
 
+	wl_display_flush(display->display);
 	wl_display_destroy(display->display);
 	free(display);
 }