agent: For SSH, robustly handling scdaemon's errors.
* agent/command-ssh.c (card_key_list): Return 0 when agent_card_serialno returns an error. (ssh_handler_request_identities): Handle errors for card listing and proceed to other cases.
- GnuPG-bug-id: T2980
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>