Previous change exposed some opportunities for further simplification in _bt_first().
Previous change exposed some opportunities for further simplification
in _bt_first().

tpostgres-projects/tPostgres,CraigHarris/gpdb,oberstet/postgres-xl,yuanzhao/gpdb,Chibin/gpdb,edespino/gpdb,xuegang/gpdb,Chibin/gpdb,adam8157/gpdb,xuegang/gpdb,greenplum-db/gpdb,Quikling/gpdb,cjcjameson/gpdb,pavanvd/postgres-xl,cjcjameson/gpdb,pavanvd/postgres-xl,janebeckman/gpdb,tpostgres-projects/tPostgres,Postgres-XL/Postgres-XL,kmjungersen/PostgresXL,ashwinstar/gpdb,atris/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,pavanvd/postgres-xl,xuegang/gpdb,kaknikhil/gpdb,royc1/gpdb,Quikling/gpdb,postmind-net/postgres-xl,0x0FFF/gpdb,kaknikhil/gpdb,snaga/postgres-xl,edespino/gpdb,foyzur/gpdb,jmcatamney/gpdb,zeroae/postgres-xl,xinzweb/gpdb,0x0FFF/gpdb,adam8157/gpdb,kaknikhil/gpdb,Quikling/gpdb,royc1/gpdb,kaknikhil/gpdb,lintzc/gpdb,rvs/gpdb,pavanvd/postgres-xl,oberstet/postgres-xl,CraigHarris/gpdb,lpetrov-pivotal/gpdb,rvs/gpdb,rvs/gpdb,chrishajas/gpdb,yazun/postgres-xl,janebeckman/gpdb,zeroae/postgres-xl,jmcatamney/gpdb,atris/gpdb,randomtask1155/gpdb,50wu/gpdb,zeroae/postgres-xl,lintzc/gpdb,chrishajas/gpdb,janebeckman/gpdb,xinzweb/gpdb,chrishajas/gpdb,Quikling/gpdb,rvs/gpdb,rvs/gpdb,cjcjameson/gpdb,royc1/gpdb,ahachete/gpdb,snaga/postgres-xl,janebeckman/gpdb,greenplum-db/gpdb,janebeckman/gpdb,royc1/gpdb,oberstet/postgres-xl,lisakowen/gpdb,chrishajas/gpdb,tangp3/gpdb,rubikloud/gpdb,rubikloud/gpdb,randomtask1155/gpdb,rubikloud/gpdb,edespino/gpdb,janebeckman/gpdb,Quikling/gpdb,royc1/gpdb,edespino/gpdb,Postgres-XL/Postgres-XL,kaknikhil/gpdb,greenplum-db/gpdb,xinzweb/gpdb,postmind-net/postgres-xl,rvs/gpdb,chrishajas/gpdb,CraigHarris/gpdb,lisakowen/gpdb,adam8157/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,zaksoup/gpdb,yuanzhao/gpdb,tangp3/gpdb,techdragon/Postgres-XL,atris/gpdb,ovr/postgres-xl,yuanzhao/gpdb,foyzur/gpdb,0x0FFF/gpdb,adam8157/gpdb,rubikloud/gpdb,ashwinstar/gpdb,xinzweb/gpdb,kaknikhil/gpdb,0x0FFF/gpdb,jmcatamney/gpdb,lisakowen/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,0x0FFF/gpdb,tpostgres-projects/tPostgres,rvs/gpdb,postmind-net/postgres-xl,Quikling/gpdb,jmcatamney/gpdb,adam8157/gpdb,foyzur/gpdb,kmjungersen/PostgresXL,ovr/postgres-xl,cjcjameson/gpdb,kaknikhil/gpdb,xuegang/gpdb,rubikloud/gpdb,lisakowen/gpdb,kaknikhil/gpdb,arcivanov/postgres-xl,adam8157/gpdb,arcivanov/postgres-xl,Postgres-XL/Postgres-XL,CraigHarris/gpdb,lpetrov-pivotal/gpdb,snaga/postgres-xl,Chibin/gpdb,chrishajas/gpdb,chrishajas/gpdb,cjcjameson/gpdb,yazun/postgres-xl,yazun/postgres-xl,Chibin/gpdb,royc1/gpdb,ahachete/gpdb,ahachete/gpdb,tangp3/gpdb,CraigHarris/gpdb,rvs/gpdb,zaksoup/gpdb,edespino/gpdb,edespino/gpdb,randomtask1155/gpdb,zaksoup/gpdb,Chibin/gpdb,lintzc/gpdb,xuegang/gpdb,ashwinstar/gpdb,lpetrov-pivotal/gpdb,cjcjameson/gpdb,foyzur/gpdb,kmjungersen/PostgresXL,arcivanov/postgres-xl,Chibin/gpdb,yuanzhao/gpdb,royc1/gpdb,atris/gpdb,yazun/postgres-xl,chrishajas/gpdb,50wu/gpdb,rubikloud/gpdb,greenplum-db/gpdb,atris/gpdb,zaksoup/gpdb,zeroae/postgres-xl,atris/gpdb,yuanzhao/gpdb,0x0FFF/gpdb,tangp3/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,arcivanov/postgres-xl,rvs/gpdb,ashwinstar/gpdb,zaksoup/gpdb,lpetrov-pivotal/gpdb,lpetrov-pivotal/gpdb,greenplum-db/gpdb,oberstet/postgres-xl,lintzc/gpdb,zaksoup/gpdb,edespino/gpdb,ahachete/gpdb,janebeckman/gpdb,zaksoup/gpdb,yazun/postgres-xl,CraigHarris/gpdb,xinzweb/gpdb,arcivanov/postgres-xl,randomtask1155/gpdb,yuanzhao/gpdb,adam8157/gpdb,CraigHarris/gpdb,adam8157/gpdb,Quikling/gpdb,50wu/gpdb,jmcatamney/gpdb,ovr/postgres-xl,snaga/postgres-xl,50wu/gpdb,xuegang/gpdb,ahachete/gpdb,jmcatamney/gpdb,snaga/postgres-xl,lisakowen/gpdb,Quikling/gpdb,janebeckman/gpdb,greenplum-db/gpdb,xinzweb/gpdb,ahachete/gpdb,lintzc/gpdb,50wu/gpdb,Quikling/gpdb,kaknikhil/gpdb,rubikloud/gpdb,atris/gpdb,tangp3/gpdb,randomtask1155/gpdb,ashwinstar/gpdb,lpetrov-pivotal/gpdb,rvs/gpdb,Postgres-XL/Postgres-XL,lisakowen/gpdb,cjcjameson/gpdb,xinzweb/gpdb,janebeckman/gpdb,CraigHarris/gpdb,0x0FFF/gpdb,zaksoup/gpdb,cjcjameson/gpdb,oberstet/postgres-xl,foyzur/gpdb,ovr/postgres-xl,ahachete/gpdb,xinzweb/gpdb,jmcatamney/gpdb,lisakowen/gpdb,foyzur/gpdb,tangp3/gpdb,kaknikhil/gpdb,lintzc/gpdb,techdragon/Postgres-XL,lpetrov-pivotal/gpdb,techdragon/Postgres-XL,tangp3/gpdb,postmind-net/postgres-xl,foyzur/gpdb,50wu/gpdb,edespino/gpdb,CraigHarris/gpdb,rubikloud/gpdb,randomtask1155/gpdb,jmcatamney/gpdb,tpostgres-projects/tPostgres,lintzc/gpdb,Chibin/gpdb,lisakowen/gpdb,xuegang/gpdb,kmjungersen/PostgresXL,postmind-net/postgres-xl,atris/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,Chibin/gpdb,edespino/gpdb,ashwinstar/gpdb,ahachete/gpdb,randomtask1155/gpdb,xuegang/gpdb,kmjungersen/PostgresXL,zeroae/postgres-xl,Postgres-XL/Postgres-XL,ashwinstar/gpdb,Chibin/gpdb,janebeckman/gpdb,tangp3/gpdb,0x0FFF/gpdb,Chibin/gpdb,arcivanov/postgres-xl,tpostgres-projects/tPostgres,xuegang/gpdb,royc1/gpdb,pavanvd/postgres-xl,lintzc/gpdb,foyzur/gpdb,edespino/gpdb,Quikling/gpdb,50wu/gpdb,ovr/postgres-xl,randomtask1155/gpdb,lintzc/gpdb,50wu/gpdb,lpetrov-pivotal/gpdb