Also require signing config when no mode is set

In this situation the milter will arbitrarily decide which mode to use
based on the IP, so it needs all of the signing bits to be defined.

openarc/openarc.c

@@ -1468,7 +1468,10 @@ arcf_config_load(struct config *data, struct arcf_config *conf,
 			conf->conf_signalg = ARC_SIGN_RSASHA256;
 		}
 
-		if ((conf->conf_mode & ARC_MODE_SIGN))
+		/* No explicit mode means we might need to sign, so these are
+		 * still required.
+		 */
+		if ((!conf->conf_mode) || (conf->conf_mode & ARC_MODE_SIGN))
 		{
 			if (config_get(data, "Domain",
 			                  &conf->conf_domain,