Handle zero public keys hash

See Lasse's comment on my PR for context.

Look for "TODO(#5862)" in the codebase.

For many of the derivation and decryption functions 0 will be a breaking value so it is simply reject in many cases, the remaining will for now be up to the application unless we figure that it is sufficiently painful to deal with at a later point, for example like the address(0) of signature recovery in solidity .