avcodec/cavsdec: Fix runtime error: signed integer overflow: 31 + 2147483640 cannot be represented in type 'int'

Fixes: 1506/clusterfuzz-testcase-minimized-5401272918212608

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

libavcodec/cavsdec.c

@@ -684,7 +684,7 @@ static int decode_mb_i(AVSContext *h, int cbp_code)
     }
     h->cbp = cbp_tab[cbp_code][0];
     if (h->cbp && !h->qp_fixed)
-        h->qp = (h->qp + get_se_golomb(gb)) & 63; //qp_delta
+        h->qp = (h->qp + (unsigned)get_se_golomb(gb)) & 63; //qp_delta
 
     /* luma intra prediction interleaved with residual decode/transform/add */
     for (block = 0; block < 4; block++) {