Fix a coverity issue in dblink
Fix a coverity issue in dblink

It's safe actually because the functions we created have two arguments
at most. Fix it anyway in case three arguments functions are introduced
in future.

/tmp/build/0e1b53a0/gpdb_src/contrib/dblink/dblink.c: 241 in dblink_connect()

________________________________________________________________________________________________________
*** CID 163942:  Null pointer dereferences  (FORWARD_NULL)
/tmp/build/0e1b53a0/gpdb_src/contrib/dblink/dblink.c: 241 in dblink_connect()
235      * Create a persistent connection to another database
236      */
237     PG_FUNCTION_INFO_V1(dblink_connect);
238     Datum
239     dblink_connect(PG_FUNCTION_ARGS)
240     {
>>>     CID 163942:  Null pointer dereferences  (FORWARD_NULL)
>>>     Assigning: "connstr" = "NULL".
241             char       *connstr = NULL;
242             char       *connname = NULL;
243             char       *msg;
244             PGconn     *conn = NULL;
245             remoteConn *rconn = NULL;
246

Signed-off-by: Adam Lee <b42a6d93d796915222f6ffb2ffdd6137d93c1cdb@pivotal.io>
Signed-off-by: Yuan Zhao <9640a31789aee25cf713d8aa6fe964eb05bab72b@pivotal.io>

lisakowen/gpdb,janebeckman/gpdb,yuanzhao/gpdb,adam8157/gpdb,xinzweb/gpdb,edespino/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,lisakowen/gpdb,yuanzhao/gpdb,50wu/gpdb,greenplum-db/gpdb,rvs/gpdb,Quikling/gpdb,Chibin/gpdb,cjcjameson/gpdb,Chibin/gpdb,edespino/gpdb,cjcjameson/gpdb,Quikling/gpdb,lisakowen/gpdb,Quikling/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,kaknikhil/gpdb,Quikling/gpdb,janebeckman/gpdb,rvs/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,rvs/gpdb,rvs/gpdb,lisakowen/gpdb,jmcatamney/gpdb,janebeckman/gpdb,kaknikhil/gpdb,lisakowen/gpdb,ashwinstar/gpdb,Quikling/gpdb,rvs/gpdb,adam8157/gpdb,Quikling/gpdb,cjcjameson/gpdb,edespino/gpdb,janebeckman/gpdb,jmcatamney/gpdb,xinzweb/gpdb,Quikling/gpdb,50wu/gpdb,Quikling/gpdb,adam8157/gpdb,rvs/gpdb,jmcatamney/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,edespino/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,janebeckman/gpdb,edespino/gpdb,cjcjameson/gpdb,kaknikhil/gpdb,Chibin/gpdb,rvs/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,janebeckman/gpdb,edespino/gpdb,yuanzhao/gpdb,Chibin/gpdb,adam8157/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,xinzweb/gpdb,Chibin/gpdb,ashwinstar/gpdb,rvs/gpdb,kaknikhil/gpdb,janebeckman/gpdb,50wu/gpdb,greenplum-db/gpdb,Chibin/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,janebeckman/gpdb,xinzweb/gpdb,edespino/gpdb,cjcjameson/gpdb,50wu/gpdb,lisakowen/gpdb,edespino/gpdb,rvs/gpdb,50wu/gpdb,adam8157/gpdb,cjcjameson/gpdb,rvs/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,Quikling/gpdb,Chibin/gpdb,jmcatamney/gpdb,adam8157/gpdb,Chibin/gpdb,janebeckman/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,Chibin/gpdb,lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,kaknikhil/gpdb,50wu/gpdb,cjcjameson/gpdb,xinzweb/gpdb,ashwinstar/gpdb,edespino/gpdb,janebeckman/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,Quikling/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,edespino/gpdb,yuanzhao/gpdb,Chibin/gpdb,kaknikhil/gpdb