OSV-2020-2259 Stack-buffer-overflow in ot::MeshCoP::ChannelMaskEntry::GetMask

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=28556 Crash type: Stack-buffer-overflow READ 4 Crash state: ot::MeshCoP::ChannelMaskEntry::GetMask ot::MeshCoP::ChannelMaskTlv::GetChannelMask ot::MeshCoP::Dataset::ConvertTo...