avcodec/ra144: Fix undefined integer overflow in add_wav()

Fixes: signed integer overflow: -26884 * 91439 cannot be represented in type 'int'
Fixes: 9687/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RA_144_fuzzer-4995588121690112

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

libavcodec/ra144.c

@@ -1516,7 +1516,7 @@ static void add_wav(int16_t *dest, int n, int skip_first, int *m,
 
     if (v[0]) {
         for (i=0; i < BLOCKSIZE; i++)
-            dest[i] = (s1[i]*v[0] + s2[i]*v[1] + s3[i]*v[2]) >> 12;
+            dest[i] = ((int)(s1[i]*(unsigned)v[0]) + s2[i]*v[1] + s3[i]*v[2]) >> 12;
     } else {
         for (i=0; i < BLOCKSIZE; i++)
             dest[i] = (             s2[i]*v[1] + s3[i]*v[2]) >> 12;