Fixes: signed integer overflow: 1603085316 + 1238786562 cannot be represented in type 'int'
Fixes: 16203/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RALF_fuzzer-5086088934195200

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