avcodec/dirac_dwt_template: Fix undefined behavior in interleave()

Fixes: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int'
Fixes: 8697/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DIRAC_fuzzer-5197148130902016

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

libavcodec/dirac_dwt_template.c

@@ -57,8 +57,8 @@ static av_always_inline void RENAME(interleave)(TYPE *dst, TYPE *src0, TYPE *src
 {
     int i;
     for (i = 0; i < w2; i++) {
-        dst[2*i  ] = (src0[i] + add) >> shift;
-        dst[2*i+1] = (src1[i] + add) >> shift;
+        dst[2*i  ] = (src0[i] + (unsigned)add) >> shift;
+        dst[2*i+1] = (src1[i] + (unsigned)add) >> shift;
     }
 }