Fixes: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int'
Fixes: 19950/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_BINKAUDIO_DCT_fuzzer-5765514337189888

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