title: ExcelDataReader.AsDataSet not working
body: <p>I'm using ExcelDataReader v.2.1. library to read both xls and xlsx files in my C# project. This way:</p>
  
  <pre><code>FileStream stream = File.Open(filePath, FileMode.Open, FileAccess.Read);
  IExcelDataReader excelReader;
  
  string extension = Path.GetExtension(filePath);
  
  if (extension == ".xls")
  {
      excelReader = ExcelReaderFactory.CreateBinaryReader(stream);
  }
  else if (extension == ".xlsx")
  {
      excelReader = ExcelReaderFactory.CreateOpenXmlReader(stream);
  }
  else
  {
      throw new NotSupportedException("Wrong file extension");
  }
  
  return excelReader;
  </code></pre>
  
  <p>Then, I use "AsDataSet" method to get a filled DataSet:</p>
  
  <pre><code>_dataSet = GetDataReader(_options.Filepath).AsDataSet();
  </code></pre>
  
  <p>It works fine most of the times, but, with some XLSX files, it only reads the first column.
  I've been looking at excelReader instance with a Watch and I saw that it actually gets all the values of the Excel, but then, when using the AsDataSet method, it only reads the first column.</p>
  
  <p>Do you know what can be going wrong here? Do you think it could be a "AsDataSet" method bug?</p>