avcodec/ffwavesynth: Fix integer overflows in pink noise addition

Fixes: signed integer overflow: -1795675744 + -1926578528 cannot be represented in type 'int'
Fixes: 17741/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFWAVESYNTH_fuzzer-5131336402075648

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 7916b6863c)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ffwavesynth.c

@@ -377,7 +377,7 @@ static void wavesynth_synth_sample(struct wavesynth_context *ws, int64_t ts,
                 in->dphi += in->ddphi;
                 break;
             case WS_NOISE:
-                val = amp * pink;
+                val = amp * (unsigned)pink;
                 break;
             default:
                 val = 0;
@@ -385,7 +385,7 @@ static void wavesynth_synth_sample(struct wavesynth_context *ws, int64_t ts,
         all_ch |= in->channels;
         for (c = in->channels, cv = channels; c; c >>= 1, cv++)
             if (c & 1)
-                *cv += val;
+                *cv += (unsigned)val;
     }
     val = (int32_t)lcg_next(&ws->dither_state) >> 16;
     for (c = all_ch, cv = channels; c; c >>= 1, cv++)