avcodec/ffwavesynth: Fix integer overflow in wavesynth_synth_sample / WS_SINE

Fixes: signed integer overflow: -1429092 * -32596 cannot be represented in type 'int'
Fixes: 24419/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFWAVESYNTH_fuzzer-5157849974702080

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit a0da95df77)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ffwavesynth.c

@@ -373,7 +373,7 @@ static void wavesynth_synth_sample(struct wavesynth_context *ws, int64_t ts,
         in->amp  += in->damp;
         switch (in->type) {
             case WS_SINE:
-                val = amp * ws->sin[in->phi >> (64 - SIN_BITS)];
+                val = amp * (unsigned)ws->sin[in->phi >> (64 - SIN_BITS)];
                 in->phi  += in->dphi;
                 in->dphi += in->ddphi;
                 break;