HIVE-6841: Vectorized execution throws NPE for partitioning columns with __HIVE_DEFAULT_PARTITION__ (reviewd by Hari, Ashutosh)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/branch-0.13@1585557 13f79535-47bb-0310-9956-ffa450edef68