Add belts-and-suspenders check for victum tuple identification
Add belts-and-suspenders check for victum tuple identification

Since overflow_tuple() cannot handle a negative value for victim_lp_len,
ensure that we have found a victim before continuing. Even though this
should be rare, being extra careful in datapage rewriting seems like a
good idea.

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