[Bug] `GetCellsByDefinedName` does not pass optional `worksheetIndex ` onward

[Smurf-IV]

```
public IEnumerable<Cell> GetCellsByDefinedName(string definedName, int? worksheetIndex = null)
    {
        var cells = new List<Cell>();
        var cellRanges = GetCellRangesByDefinedName(definedName) as List<List<Cell>>;