Don't segfault if the ais group is not found.

git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@1711 fd59a12c-fef9-0310-b244-a6a79926bd2f

exec/main.c

@@ -293,7 +293,7 @@ static void aisexec_gid_determine (struct main_config *main_config)
 	struct group *group;
 	group = getgrnam (main_config->group);
 	if (group == 0) {
-		log_printf (LOG_LEVEL_ERROR, "ERROR: The '%s' group is not found in /etc/group, please read the documentation.\n", group->gr_name);
+		log_printf (LOG_LEVEL_ERROR, "ERROR: The '%s' group is not found in /etc/group, please read the documentation.\n", main_config->group);
 		corosync_exit_error (AIS_DONE_GID_DETERMINE);
 	}
 	gid_valid = group->gr_gid;