vout: add a warning

pl_Get() can only be used in interfaces, playlist and ML code.

src/video_output/event.h

@@ -43,6 +43,7 @@ static inline void vout_SendEventClose(vout_thread_t *vout)
     /* Ask to stop
      * FIXME works only for input handled by the playlist
      */
+#warning FIXME: remove pl_Get
     playlist_t *playlist = pl_Get(vout);
     playlist_Stop(playlist);
 }