avcodec/dca_xll: Fix runtime error: signed integer overflow: 2147286116 +...

avcodec/dca_xll: Fix runtime error: signed integer overflow: 2147286116 + 6298923 cannot be represented in type 'int'

Fixes: 732/clusterfuzz-testcase-4872990070145024

See: [FFmpeg-devel] [PATCH 2/6] avcodec/dca_xll: Fix runtime error: signed integer overflow: 2147286116 + 6298923 cannot be represented in type 'int'
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/dca_xll.c

@@ -1312,7 +1312,7 @@ static int combine_residual_frame(DCAXllDecoder *s, DCAXllChSet *c)
         } else {
             // No downmix scaling
             for (n = 0; n < nsamples; n++)
-                dst[n] += (src[n] + round) >> shift;
+                dst[n] += (unsigned)((src[n] + round) >> shift);
         }
     }