Fixes: signed integer overflow: 2145417478 + 76702564 cannot be represented in type 'int'
Fixes: 20313/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RA_144_fuzzer-5734487724130304

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit abb5762e)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>