Fixes: memleaks
Fixes: 21084/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5655975492321280

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>