title: Table Header is not showing in exported PDF/EXCEL if I am using column search option in dataTables
body: <p>I am a new user to dataTables.
  I am exporting PDF/EXCEL by using buttons. Here facing one issue.
  if I am using column search option then header columns are not visible in PDF/EXCEL.
  Can u please help me. Thanks in advance.</p>
  
  <p>here is my code:</p>
  
  <pre><code>$('#exampleList thead tr#filterrow th').each( function (exampleListId) {
  var title = $('#exampleList thead th').eq( $(this).index() ).text();
  
  $(this).html( '&lt;input type="text" style="width: 90%;"  id="exmpl'+exampleListId+'" placeholder="Search '+title+'"/&gt;' ).focusout(function (e) {
      window.flagfocus=true; 
      window.searchColDets.push({
      "column": e.target.id,
      "value": e.target.value
      });             
    });       
  });
  
  $('#exampleList').DataTable({
      data: partyListArr,
      "order": [[ 2, "asc" ]],
      "pagingType": "full_numbers",
      "stateSave": true,
      "scrollY":   410,
      "scrollCollapse": true,
      "lengthMenu" : [[25, 50, 100, -1], [25, 50, 100, "All"]],
      "Filter": true,
      "destroy" : true,
      "deferRender": true,
  
      "sDom":'T&lt;"toolbar"&gt;Blrtip',      
      buttons: [
  
              {
                  extend: 'pdfHtml5',
                  text: 'Save current page',
                  orientation: 'landscape',
                  pageSize: 'LEGAL',                  
                  exportOptions: {                        
                      modifier: {
                          page: 'current'
                      },
                      columns: [ 1, 2, 3, 4, 5, 6, 7, 8, 10 ],                         
                  },                 
              },
              {
                  extend: 'excelHtml5',
                  exportOptions: {
                      columns: [ 1, 2, 3, 4, 5, 6, 7, 8, 10 ]
                  }
              },             
          ]
   }); //Close datatable
  </code></pre>