title: xlsxwriter is creating a corrupted file
body: <p>I'm using this code to test xlswriter functionnalitues.</p>
  
  <pre><code>    import xlsxwriter 
  # -*- coding: utf-8-sig-*-
  workbook = xlsxwriter.Workbook("filename.xlsx")
  worksheet = workbook.add_worksheet()
  worksheet.add_table(0,0, 1, 11,{'columns': [{'header': 'ID'},
                                            {'header': '1'},
                                            {'header': u'ééé'},
                                            {'header': 'M'},
                                            {'header': 'C'},
                                            {'header': 'P'},
                                            {'header': u'o'},
                                            {'header': 'Pe'},
                                            {'header': 'F'},
                                            {'header': u'l'},
                                            {'header': 'C'},
                                            {'header': 'f'}
                                            ]})
  workbook.close()
  </code></pre>
  
  <p>Excel is complaining about the file being corrputed. If I accept the repair I got the content as expected.</p>
  
  <p>Update:
  I have the same problem with this minimalistic code:</p>
  
  <pre><code>import xlsxwriter 
  
  
  
  workbook = xlsxwriter.Workbook("filename.xlsx")
  worksheet = workbook.add_worksheet("hi")
  worksheet.add_table(0,0, 1, 2,{'columns': [{'header': 'ID'},
                                            {'header': '1'},
                                            {'header': '1'}]})
  workbook.close()
  </code></pre>