HDFS scan operator may not always return diags info with error entry

[Justin Du]

This problem was found when examining the esp core files. The code dump was due to the reason at these lines in sql/executor/ex_tuple_flow.cpp:

    349 ComDiagsArea * da = src_entry->getDiagsArea();
    350 ex_assert(da, "We have a Q_SQLERROR in Tupleflow but no diags area");
    351

Further analysis indicates that ExHdfsScanTcb::work() method inserted the Q_SQLERROR entry to its parent up queue without attaching the diags area with it.

When the work method inserts a Q_SQLERROR entry, it expects that the head entry of the parent down queue contains the diags area, which was populated in other steps prior to the HANDLE_ERROR step, or the workAtp_ should have one. Otherwise, it could return that entry without populated the atp_ diags area of the entry.

The more suspicious area is at line 820 of sql/executor/ExHdfsScan.cpp when ExHdfsScanTcb::extractAndTransformAsciiSourceToSqlRow() call returns error but without populating the diagsArea of workAtp_.