Fix Reader Bugs

[YeGaSoft]

• Fix Bugs at ReadCell() when Cell.CellText is null (return String.Empty);
• Fix Bug where header columns will be returned in Select();

[YeGaSoft]

ReadCell Bug fixed. new string(" ") will be returned (Note: At CreateCell it'll also write new string(" "), to ensure that the entry will be created)

[YeGaSoft]

Fixed header column 'bug' in Select

[YeGaSoft]

All bugs fixed.