avcodec/dpcm: fix undefined interger overflow in wady

Fixes: signed integer overflow: -2147375930 + -133875 cannot be represented in type 'int'
Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WADY_DPCM_fuzzer-6703727013920768

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

libavcodec/dpcm.c

@@ -444,7 +444,7 @@ static int dpcm_decode_frame(AVCodecContext *avctx, AVFrame *frame,
             if (n & 0x80)
                 s->sample[idx] = sign_extend((n & 0x7f) << 9, 16);
             else
-                s->sample[idx] += s->scale * wady_table[n & 0x7f];
+                s->sample[idx] += s->scale * (unsigned)wady_table[n & 0x7f];
             *output_samples++ = av_clip_int16(s->sample[idx]);
             idx ^= stereo;
         }