standby switchover: improve archive check error handling

Explicitly log if a database connection failure caused the check
to fail.

It's unlikely this situation will be encountered, as the data directory
check will already have run and checked for connection failure, however
there's a small chance the connection could fail between checks.

repmgr-action-node.c

@@ -806,7 +806,6 @@ do_node_check(void)
 	{
 		exit_optformat_error("DB_CONNECTION",
 							 ERR_DB_CONN);
-
 	}
 
 	if (get_node_record(conn, config_file_options.node_id, &node_info) != RECORD_FOUND)