OSV-2020-353 Stack-buffer-overflow in ot::MeshCoP::Commissioner::GeneratePskc

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=19386 Crash type: Stack-buffer-overflow WRITE Crash state: ot::MeshCoP::Commissioner::GeneratePskc ot::Ncp::NcpBase::HandlePropertySetSPINELPROPMESHCOPCOMMISSIONERGENERATEPS ot::Ncp::NcpBase::HandlePropertySetForSpecialPropert...