avcodec/ffwavesynth: Fixes invalid shift with pink noise seeking

Fixes: left shift of negative value -961533698048
Fixes: 16242/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFWAVESYNTH_fuzzer-5738550670131200

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>

libavcodec/ffwavesynth.c

@@ -220,7 +220,7 @@ static void wavesynth_seek(struct wavesynth_context *ws, int64_t ts)
         int64_t pink_ts_cur  = (ws->cur_ts + PINK_UNIT - 1) & ~(PINK_UNIT - 1);
         int64_t pink_ts_next = ts & ~(PINK_UNIT - 1);
         int pos = ts & (PINK_UNIT - 1);
-        lcg_seek(&ws->pink_state, (pink_ts_next - pink_ts_cur) << 1);
+        lcg_seek(&ws->pink_state, (pink_ts_next - pink_ts_cur) * 2);
         if (pos) {
             pink_fill(ws);
             ws->pink_pos = pos;