title: csv export not working with symfony 3
body: <p>I try to do a csv export on my symfony project and i think that something is wrong because nothing happens and i have no error...??</p>
  
  <pre><code>public function exportCsv($customers)
  {
  $fileName = "export_" . date("d_m_Y") . ".csv";
  $response = new StreamedResponse();
  
  
  $response-&gt;setCallback(function() use ($customers){
      $handle = fopen('php://output', 'w+');
  
      // Nom des colonnes du CSV
      fputcsv($handle, array('Name',
          'Adress',
          'City',
          'Code'
      ), ';');
  
      //Champs
      foreach ($customers as $index =&gt; $customer)
      {
          //dump($client);die();
          fputcsv($handle,array(
              $customer-&gt;getName(),
              $customer-&gt;getAdress(),
              $customer-&gt;getCity(),
              $customer-&gt;getCode(),
          ),';');
      }
      fclose($handle);
  });
  
  
  $response-&gt;setStatusCode(200);
  $response-&gt;headers-&gt;set('Content-Type', 'text/csv; charset=utf-8', 'application/force-download');
  $response-&gt;headers-&gt;set('Content-Disposition','attachment; filename='.$fileName);
  
  
  return $response;
  
  }
  </code></pre>
  
  <p>I call this function in my controler like this:</p>
  
  <pre><code>if (isset($_POST['export']))
  {
      $export = $exp-&gt;exportCsv($customers);
  
  }
  </code></pre>
  
  <p>Have you any idea, please???</p>