Remove residual NULL-pstate handling in addRangeTableEntry.
Remove residual NULL-pstate handling in addRangeTableEntry.

Passing a NULL pstate wouldn't actually work, because isLockedRefname()
isn't prepared to cope with it; and there hasn't been any in-core code
that tries in over a decade.  So just remove the residual NULL handling.

Spotted by Coverity; analysis and patch by Michael Paquier.

ovr/postgres-xl,Postgres-XL/Postgres-XL,yazun/postgres-xl,techdragon/Postgres-XL,zeroae/postgres-xl,lisakowen/gpdb,techdragon/Postgres-XL,jmcatamney/gpdb,adam8157/gpdb,pavanvd/postgres-xl,jmcatamney/gpdb,oberstet/postgres-xl,ashwinstar/gpdb,ashwinstar/gpdb,lisakowen/gpdb,zeroae/postgres-xl,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,50wu/gpdb,ashwinstar/gpdb,ovr/postgres-xl,yazun/postgres-xl,pavanvd/postgres-xl,oberstet/postgres-xl,ovr/postgres-xl,Postgres-XL/Postgres-XL,ovr/postgres-xl,ashwinstar/gpdb,pavanvd/postgres-xl,techdragon/Postgres-XL,lisakowen/gpdb,ashwinstar/gpdb,50wu/gpdb,techdragon/Postgres-XL,zeroae/postgres-xl,oberstet/postgres-xl,Postgres-XL/Postgres-XL,adam8157/gpdb,lisakowen/gpdb,xinzweb/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,greenplum-db/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,yazun/postgres-xl,ashwinstar/gpdb,xinzweb/gpdb,50wu/gpdb,pavanvd/postgres-xl,adam8157/gpdb,oberstet/postgres-xl,lisakowen/gpdb,yazun/postgres-xl,jmcatamney/gpdb,adam8157/gpdb,jmcatamney/gpdb,Postgres-XL/Postgres-XL,xinzweb/gpdb,adam8157/gpdb,oberstet/postgres-xl,ovr/postgres-xl,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,xinzweb/gpdb,zeroae/postgres-xl,jmcatamney/gpdb,jmcatamney/gpdb,lisakowen/gpdb,yazun/postgres-xl,50wu/gpdb,50wu/gpdb,50wu/gpdb,adam8157/gpdb,xinzweb/gpdb,Postgres-XL/Postgres-XL,greenplum-db/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,zeroae/postgres-xl,xinzweb/gpdb,lisakowen/gpdb