Peg related RPC calls should error if there is no parent chain set

[wintercooled]

Currently (tested in 0.18.1.9 and 0.18.11):

If I set chain=whatever, con_has_parent_chain=0 or parentgenesisblockhash=Null in elements.conf I can still call getpeginaddress from a connected client without error and get a mainchain_address and claim_script returned.

I would have expected any peg related RPC calls to error if the parent chain is nothing.