[CBRD-24867] regression bug-fix related to DBLINK (DML and extended table specification)

[beyondykk9]

http://jira.cubrid.org/browse/CBRD-24867

Modified the code so that the queries below work properly.

○ segmentation fault
– Created in remote DB
create table t1 (a int PRIMARY KEY, b varchar(100));
insert into t1 values (1, 'abc'), (2, 'abcd'), (3, 'abcde'), (4, 'abcdef'), (5, 'abcdefg');

--create table/data in local DB
create table tbl(a int, b varchar(100));
insert into tbl values (1, 'abc'), (2, 'abcd'), (3, 'abcde'), (4, 'abcdef'), (5, 'abcdefg');

– Running on local DB – Segmentation fault (core dumped)
update tbl set b = ( select a||'sub query1' from t1@srv1 limit 1) where tbl.a=2;
delete tbl from tbl where a = (select a from t1@srv1 where a = 3 ) ;

○ segmentation fault when using set operators (union, difference, intersection)
--create table/data in local DB
create table statement_set_operators (col1 varchar(100), a int, b varchar(100));

insert into statement_set_operators(col1, a, b)
( select 'local', A.* from tbl A
union all
select 'remote', A.* from t1@srv1 A ) ;