DERBY-6674 Cleanup brittle code in ValidateCheckConstraintResultSet

Backport from trunk as

svn merge -c 1614963 https://svn.apache.org/repos/asf/db/derby/code/trunk

Patch derby-6674. Refactors the code by reusing getNextRowCore (to
avoid the redundancy) for ValidateCheckConstraintResultSet but
abstracting out the loop control, which is overridden by
ValidateCheckConstraintResultSet.



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/branches/10.11@1616511 13f79535-47bb-0310-9956-ffa450edef68