In dumpTable, re-instate the skipping logic
In dumpTable, re-instate the skipping logic

Pretty sure I removed this based on some incorrect thinking that it was
no longer possible to reach this point for a table which will not be
dumped, but that's clearly wrong.

Pointed out on IRC by Erik Rijkers.

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