avcodec/ffwavesynth: Fix integer overflow for some corner case values

Fixes: left shift of negative value -14671840
Fixes: 16000/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFWAVESYNTH_fuzzer-5145977817661440

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

libavcodec/ffwavesynth.c

@@ -301,8 +301,8 @@ static int wavesynth_parse_extradata(AVCodecContext *avc)
             default:
                 return AVERROR(EINVAL);
         }
-        in->amp0 = (int64_t)a1 << 32;
-        in->damp = (((int64_t)a2 << 32) - ((int64_t)a1 << 32)) / dt;
+        in->amp0 = (uint64_t)a1 << 32;
+        in->damp = (int64_t)(((uint64_t)a2 << 32) - ((uint64_t)a1 << 32)) / dt;
     }
     if (edata != edata_end)
         return AVERROR(EINVAL);