avcodec/apedec: Fix 2 integer overflows

Fixes: signed integer overflow: 2119056926 - -134217728 cannot be represented in type 'int'
Fixes: 18728/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5747539563511808

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

libavcodec/apedec.c

@@ -1234,7 +1234,7 @@ static void predictor_decode_mono_3950(APEContext *ctx, int count)
             p->buf = p->historybuffer;
         }
 
-        p->filterA[0] = currentA + ((int)(p->filterA[0] * 31U) >> 5);
+        p->filterA[0] = currentA + (unsigned)((int)(p->filterA[0] * 31U) >> 5);
         *(decoded0++) = p->filterA[0];
     }
 
@@ -1302,7 +1302,7 @@ static void do_apply_filter(APEContext *ctx, int version, APEFilter *f,
             else
                 *f->adaptcoeffs = 0;
 
-            f->avg += (absres - f->avg) / 16;
+            f->avg += (int)(absres - (unsigned)f->avg) / 16;
 
             f->adaptcoeffs[-1] >>= 1;
             f->adaptcoeffs[-2] >>= 1;