title: NPOI 2.1.3.1 produces corrupted XLSX files
body: <p>I'm trying to use NPOI 2.1.3.1 to create an Excel file from some database data. The file being created, though, is corrupted. Excel refuses to open it, and changing it to a ZIP and trying to extract it also causes errors in Windows and in WinRAR. Other threads I've read say to upgrade to 2.1.3.1 because it fixes something about XLSX creation, but that's not true at all. I've also read it has something to do with how it ZIPs the file, but there doesn't seem to be any ability to control that. I'm hoping someone can point me in the right direction with my code below:</p>
  
  <pre><code>public byte[] GetExcelFile(
      QueryModel query) {
      var orders = Mapper.Map&lt;IList&lt;ExcelListModel&gt;&gt;(Context.Orders.Where(
          o =&gt;
              o.DateOrdered &gt;= query.Start
              &amp;&amp; o.DateOrdered &lt;= query.End));
      var workbook = new XSSFWorkbook();
      var sheet = workbook.CreateSheet();
  
      for (int i0 = 0, l0 = orders.Count, r = 0; i0 &lt; l0; i0++) {
          var order = orders[i0];
  
          for (int i1 = 0, l1 = order.Products.Count; i1 &lt; l1; i1++, r++) {
              var row = sheet.CreateRow(r);
              var product = order.Products[i1];
  
              row.CreateCell(0).SetCellValue("");
              //  ...
              row.CreateCell(18).SetCellValue("");
          }
  
          for (int i1 = 0, l1 = order.Bonuses.Count; i1 &lt; l1; i1++, r++) {
              var row = sheet.CreateRow(r);
              var bonus = order.Bonuses[i1];
  
              row.CreateCell(0).SetCellValue("");
              //  ...
              row.CreateCell(18).SetCellValue("");
          }
      }
  
      var memoryStream = new MemoryStream();
  
      workbook.Write(memoryStream);
  
      return memoryStream.ToArray();
  }
  </code></pre>