session: Avoid memory leak of agent_socket from configuration file

Thanks oss-fuzz

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=48268

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
(cherry picked from commit aa1e136ea3)

src/session.c

@@ -301,6 +301,7 @@ void ssh_free(ssh_session session)
   SAFE_FREE(session->banner);
   SAFE_FREE(session->disconnect_message);
 
+  SAFE_FREE(session->opts.agent_socket);
   SAFE_FREE(session->opts.bindaddr);
   SAFE_FREE(session->opts.custombanner);
   SAFE_FREE(session->opts.moduli_file);