avcodec/wavarc: Avoid signed integer overflow in sample

Fixes: signed integer overflow: -2147483648 + -25122315 cannot be represented in type 'int'
Fixes: 62285/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WAVARC_fuzzer-6199806972198912

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 6009dd07bd)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/wavarc.c

@@ -374,7 +374,7 @@ static int decode_2slp(AVCodecContext *avctx,
                 for (int o = 0; o < order; o++)
                     sum += s->filter[ch][o] * (unsigned)samples[n + 70 - o - 1];
 
-                samples[n + 70] = get_srice(gb, k) + (sum >> 4);
+                samples[n + 70] = get_srice(gb, k) + (unsigned)(sum >> 4);
             }
             finished = 1;
             break;