avcodec/takdec: Fixes: integer overflow in AV_SAMPLE_FMT_U8P output

Fixes: runtime error: signed integer overflow: 2147483543 + 128 cannot be represented in type 'int'
Fixes: 2234/clusterfuzz-testcase-minimized-6266896041115648

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