Fixes: signed integer overflow: -395281576 + -1827578048 cannot be represented in type 'int'
Fixes: 16038/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_TTA_fuzzer-5646109705240576

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