Fixes: signed integer overflow: 2142077091 + 6881070 cannot be represented in type 'int'
Fixes: 22737/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WMALOSSLESS_fuzzer-5958388889681920

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 c0dfe134beefde4070d43910518b1f4a58f01794)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>