OSV-2020-22 Container-overflow in parquet::schema::Unflatten

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=20897 Crash type: Container-overflow READ 4 Crash state: parquet::schema::Unflatten parquet::FileMetaData::FileMetaDataImpl::FileMetaDataImpl parquet::FileMetaData::FileMetaData...