avformat/lrcdec: Fix memleak upon read header failure

The already parsed subtitles (contained in an FFDemuxSubtitlesQueue)
would leak if an error happened upon reading a subsequent subtitle.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit d38694cea9)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/lrcdec.c

@@ -202,6 +202,7 @@ static int lrc_read_header(AVFormatContext *s)
                 sub = ff_subtitles_queue_insert(&lrc->q, line.str + ts_strlength,
                                                 line.len - ts_strlength, 0);
                 if(!sub) {
+                    ff_subtitles_queue_clean(&lrc->q);
                     return AVERROR(ENOMEM);
                 }
                 sub->pos = pos;