OSV-2020-1976 Use-of-uninitialized-value in FLAC::Decoder::FuzzerStream::write_callback

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=16503 Crash type: Use-of-uninitialized-value Crash state: FLAC::Decoder::FuzzerStream::writecallback writeaudioframetoclient readframe...