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 e13874b9eae4e156ca1c478e6d59d3461bbdc09f)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>