avcodec/alacdsp: fix integer overflow in decorrelate_stereo()

Fixes: signed integer overflow: -16777216 * 131 cannot be represented in type 'int'
Fixes: 23835/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALAC_fuzzer-5669943160078336
Fixes: 41101/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALAC_fuzzer-4636330705944576

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

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/alacdsp.c

@@ -34,7 +34,7 @@ static void decorrelate_stereo(int32_t *buffer[2], int nb_samples,
         a = buffer[0][i];
         b = buffer[1][i];
 
-        a -= (b * decorr_left_weight) >> decorr_shift;
+        a -= (int)(b * (unsigned)decorr_left_weight) >> decorr_shift;
         b += a;
 
         buffer[0][i] = b;