avcodec/apedec: Fix integer overflow in filter_3800()

Fixes: signed integer overflow: -2147448926 + -198321 cannot be represented in type 'int'
Fixes: 48798/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5739619273015296
Fixes: 48798/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-6744428485672960

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg


Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit f05247f6)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>