avcodec/svq3: Fix runtime error: signed integer overflow: 169 * 12717677 cannot be represented in type 'int'

Fixes: 1556/clusterfuzz-testcase-minimized-5027865978470400

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

libavcodec/svq3.c

@@ -263,7 +263,7 @@ static void svq3_add_idct_c(uint8_t *dst, int16_t *block,
     int i;
 
     if (dc) {
-        dc       = 13 * 13 * (dc == 1 ? 1538 * block[0]
+        dc       = 13 * 13 * (dc == 1 ? 1538U* block[0]
                                       : qmul * (block[0] >> 3) / 2);
         block[0] = 0;
     }