HIVE-6711 : ORC maps uses getMapSize() from MapOI which is unreliable (Prasanth J via Vikram Dixit, reviewed by Gunther)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/branch-0.13@1580802 13f79535-47bb-0310-9956-ffa450edef68