Fixes: VUI extension leak
Fixes: 63004/clusterfuzz-testcase-minimized-ffmpeg_BSF_VVC_METADATA_fuzzer-4928832253329408

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>