auth: Avoid memory on error in ssh_userauth_agent_publickey()

CID 1401095

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>

src/auth.c

@@ -757,6 +757,7 @@ static int ssh_userauth_agent_publickey(ssh_session session,
     if (sig_type_c == NULL) {
         ssh_set_error(session, SSH_REQUEST_DENIED,
                       "Invalid key type (unknown)");
+        SSH_STRING_FREE(pubkey_s);
         return SSH_AUTH_DENIED;
     }
     if (!ssh_key_algorithm_allowed(session, sig_type_c)) {