standby switchover: mark successful if standby attaches later

Handle corner case where standby (demotion candidate) doesn't
attach during the main check cycle, but does at the final check,
where we'll want to mark the operation as successful.

repmgr-action-standby.c

@@ -4844,6 +4844,7 @@ do_standby_switchover(void)
 													 remote_node_record.node_name);
 		if (node_attached == NODE_ATTACHED)
 		{
+			switchover_success = true;
 			log_notice(_("switchover was successful"));
 			log_detail(_("node \"%s\" is now primary and node \"%s\" is attached as standby"),
 					   local_node_record.node_name,