StreamingRow.getLastCellNum() off-by-one and blank cells

[ms1111]

Hi! I think getLastCellNum() may be returning a value 1 more than intended.

With two columns (A and B), it returns a value of 3. (see implementation below - it's returning size() + 1).

With a blank column - let's say we have A populated, B blank, C blank, and D populated - it's not looking for the highest valued column index, just the number of populated columns, so the result there is not correct either.

  /**
   * Gets the index of the last cell contained in this row <b>PLUS ONE</b>.
   * 
   * @return short representing the last logical cell in the row <b>PLUS ONE</b>,
   *   or -1 if the row does not contain any cells.
   */
  @Override
  public short getLastCellNum() {
    return (short) (cellMap.size() == 0 ? -1 : cellMap.size() + 1);
  }

Workaround, to get the number of cells in a row with either XLSX streaming or regular POI:

    private int numCellsInRow(Row row) {
        if (row instanceof StreamingRow) {
            List<Integer> colIndexes = new ArrayList<>(((StreamingRow) row).getCellMap().keySet());
            if (colIndexes.size() < 1) {
                return 0;
            }
            colIndexes.sort(null);
            return colIndexes.get(colIndexes.size()-1) + 1;
        }
        else {
            // HSSFRow.getLastCellNum() returns the 1-based index of the last cell, or -1
            return (row.getLastCellNum() < 1) ? 0 : row.getLastCellNum();
        }
    }

[ms1111]

Fixed by #61