Fixes: out of array access
Fixes: 30135/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PBM_fuzzer-4997145650397184
Fixes: 30208/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PGMYUV_fuzzer-5605891665690624.fuzz
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 5314a4996cc76e2a8534c74a66f5181e95ac64fc)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>