vcodec/apedec: Fix integer overflow in filter_3800()

Fixes: signed integer overflow: 2021654528 + 2032575680 cannot be represented in type 'int'
Fixes: 16270/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5732438816325632

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

libavcodec/apedec.c

@@ -842,7 +842,7 @@ static av_always_inline int filter_fast_3320(APEPredictor *p,
 }
 
 static av_always_inline int filter_3800(APEPredictor *p,
-                                        const int decoded, const int filter,
+                                        const unsigned decoded, const int filter,
                                         const int delayA,  const int delayB,
                                         const int start,   const int shift)
 {