This requires us to pre-parse the skip data, as we want to
detect this before allocating all the arrays

Fixes: Timeout
Fixes: 9708/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WMV2_fuzzer-5729709861109760

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