agent: Recover support CHECK_OWN_SOCKET_INTERVAL == 0.
* agent/gpg-agent.c (handle_connections): Only spawn the thread when CHECK_OWN_SOCKET_INTERVAL > 0. [CHECK_OWN_SOCKET_INTERVAL == 0] (check_own_socket_pid_cb) (do_check_own_socket, check_own_socket_thread): Ifdef out.
- GnuPG-bug-id: T6692
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>