video_output: copy the redisplay return value in displayed.date code

The code is logically equivalent. It will allow some simplifications later.

src/video_output/video_output.c

@@ -1433,6 +1433,11 @@ static vlc_tick_t DisplayPicture(vout_thread_sys_t *vout)
         date_refresh = sys->displayed.date + VOUT_REDISPLAY_DELAY - render_delay;
         refresh = date_refresh <= system_now;
         render_now = refresh;
+        if (!first && !refresh && next == NULL) {
+            // nothing changed, wait until the next deadline or a control
+            vlc_tick_t max_deadline = vlc_tick_now() + VOUT_REDISPLAY_DELAY;
+            return __MIN(date_refresh, max_deadline);
+        }
     }
     else
     {