OSV-2021-581 UNKNOWN READ in unsigned short flatbuffers::ReadScalar<unsigned short>

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=32647 Crash type: UNKNOWN READ Crash state: unsigned short flatbuffers::ReadScalar flatbuffers::Table::GetOptionalFieldOffset flatbuffers::Table::CheckField...