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 f3c63e67bb00fa7d96595203d01a576df651e275)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>