Selection among multiple keys fails

[Mathias Herberts]

When an agent is configured with multiple keys AND all those keys are accepted on a remote host, pressing 'x' (cancel) when asked to confirm signature with the first key, the agent fails to request signature from the following keys.

The use case is when multiple keys are listed in an authorized_keys file with different commands, the target command is determined by the key used to connect, hence the importance to be able to deny signatures until the signature by the wanted key is requested.