lavfi/buffersink: check av_frame_ref() failure.

libavfilter/buffersink.c

@@ -137,7 +137,8 @@ int attribute_align_arg av_buffersink_get_frame_flags(AVFilterContext *ctx, AVFr
 
     if (flags & AV_BUFFERSINK_FLAG_PEEK) {
         cur_frame = *((AVFrame **)av_fifo_peek2(buf->fifo, 0));
-        av_frame_ref(frame, cur_frame); /* TODO check failure */
+        if ((ret = av_frame_ref(frame, cur_frame)) < 0)
+            return ret;
     } else {
         av_fifo_generic_read(buf->fifo, &cur_frame, sizeof(cur_frame), NULL);
         av_frame_move_ref(frame, cur_frame);