HIVE-5357: ReduceSinkDeDuplication optimizer pick the wrong keys in pRS-cGBYm-cRS-cGBYr scenario when there are distinct keys in child GBY (Chun Chen via Ashutosh Chauhan)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/branch-0.12@1527843 13f79535-47bb-0310-9956-ffa450edef68