Fix uninitialized variable in pgrowlocks
Fix uninitialized variable in pgrowlocks

Because the variable rel is only used in if (SRF_IS_FIRSTCALL()) branch,
we should move it's declaration into this branch (suggested by Hubert Zhang).

xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,adam8157/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,50wu/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,50wu/gpdb,jmcatamney/gpdb,adam8157/gpdb,jmcatamney/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,adam8157/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,jmcatamney/gpdb