compositor: initialize ret in repaint_timer_handler

If output_list of compositor is empty, value of
ret is read without initialization.

Signed-off-by: Emre Ucan <eucan@de.adit-jv.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

libweston/compositor.c

@@ -2457,7 +2457,7 @@ output_repaint_timer_handler(void *data)
 	struct weston_output *output;
 	struct timespec now;
 	void *repaint_data = NULL;
-	int ret;
+	int ret = 0;
 
 	weston_compositor_read_presentation_clock(compositor, &now);