[security] remove panic from from_proto function
[security] remove panic from from_proto function

This paths should be reachable as the field is optional. I don't think we should have panics in `from_proto` functions.

libra/libra,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core