The check is based on not infinite looping. It is likely
a more strict check can be done

Fixes: Infinite loop
Fixes: 62473/clusterfuzz-testcase-minimized-ffmpeg_BSF_EVC_FRAME_MERGE_fuzzer-5719883750703104
Fixes: 62765/clusterfuzz-testcase-minimized-ffmpeg_dem_EVC_fuzzer-6448531252314112
Fixes: 63378/clusterfuzz-testcase-minimized-ffmpeg_dem_MPEGPS_fuzzer-6504993844494336

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: "Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff Engineer/Samsung Electronics" <d.kozinski@samsung.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>