Fixes: memleak
Fixes: 15528/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_STL_fuzzer-5735993371525120
Fixes: 15792/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SAMI_fuzzer-5737754232619008
Fixes: 16008/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SSA_fuzzer-5650582821404672

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>