Fix [first N] issue in ExHdfsScanTcb (hive scan)

This change corrects processing of GET_N in ExHdfsScanTcb, in cases
where the operator scans multiple parts of an HDFS file.

Closes-Bug: #1355477

Change-Id: I931d65a515a89c3e8a5bb12348978d7fd36f047c
Merge "Fix [first N] issue in ExHdfsScanTcb (hive scan)"