public double getDouble(int elementNum) {
    return asScratchIntervalDayTime(elementNum).getDouble();
  }
Return a row's HiveIntervalDayTime.getDouble() value.
We assume the entry has already been NULL checked and isRepeated adjusted.
@param elementNum
@return
storage-api/src/java/org/apache/hadoop/hive/ql/exec/vector/IntervalDayTimeColumnVector.java