Fixes: Segfault
Fixes: 17991/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HCOM_fuzzer-5647235349479424

Also fixes related memleak

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