src/video_output/video_output.c: Wait till command has been processed.

Wait till the stop command has been processed by the thread before continuing.

src/video_output/video_output.c

@@ -235,6 +235,7 @@ no_reuse:
         cmd.u.cfg = cfg;
 
         vout_control_Push(&vout->p->control, &cmd);
+        vout_control_WaitEmpty(&vout->p->control);
         }
         vout_CloseAndRelease(vout);