Follow up to the comment here: paritytech/polkadot#1740 (comment)

The behaviour of the has_keys would be slow in cases such as:

https://github.com/paritytech/polkadot/blob/9ce9eccae4faa7935bbca9a4200e0978168a46f9/node/network/availability-distribution/src/lib.rs#L582-L586

where the list of keys is iterated so that the first key found is returned. However, in case of a remote signer, this loop would be quite slow.

has_keys behaviour should be modified so that the index of the first element found is returned so that this index can be used to return the public key.