OSV-2020-2247 Stack-buffer-overflow in ot::MeshCoP::ChannelMaskEntryBase::GetEntrySize

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=28315 Crash type: Stack-buffer-overflow READ 1 Crash state: ot::MeshCoP::ChannelMaskEntryBase::GetEntrySize ot::MeshCoP::ChannelMaskEntryBase::GetNext ot::MeshCoP::ChannelMaskBaseTlv::IsValid...