avcodec/wavpack: Fix integer overflow in wv_unpack_stereo()

Fixes: runtime error: signed integer overflow: 2147483531 + 16384 cannot be represented in type 'int'
Fixes: 6615/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WAVPACK_fuzzer-5165715515506688

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

libavcodec/wavpack.c

@@ -452,7 +452,7 @@ static inline int wv_unpack_stereo(WavpackFrameContext *s, GetBitContext *gb,
                 if (type != AV_SAMPLE_FMT_S16P)
                     R2 = R + ((s->decorr[i].weightB * (int64_t)L2 + 512) >> 10);
                 else
-                    R2 = R + ((int)(s->decorr[i].weightB * (unsigned)L2 + 512) >> 10);
+                    R2 = R + (unsigned)((int)(s->decorr[i].weightB * (unsigned)L2 + 512) >> 10);
                 UPDATE_WEIGHT_CLIP(s->decorr[i].weightB, s->decorr[i].delta, L2, R);
                 R                        = R2;
                 s->decorr[i].samplesA[0] = R;