Values larger would fail subsequent tests.

Fixes: signed integer overflow: 5 + 2147483646 cannot be represented in type 'int'
Fixes: 16966/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-5695709549953024

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