ssh: Fix possible infinite loop in case of an read error.
* agent/command-ssh.c (ssh_handler_add_identity): Handle other errors than EOF.
(cherry picked from commit 7385e1babf6eef586c79ad23f8e541aaf608c4e5)
- GnuPG-bug-id: T4221
- Signed-off-by: Werner Koch <wk@gnupg.org>