title: Symfony 3 - File edit form doesn't display photo name
body: <p>I have a problem with editing an entity that has a file.
  I followed the Symfony documentation for uploading a file and it works fine.
  At creation my file is stored well in my upload folder and the encrypted name stored in database.</p>
  
  <p>For the edition I followed the documentation so as not to have any error, I quote:</p>
  
  <blockquote>
    <p>When creating a form to edit an already persisted item, the file form type still expects a File instance. As the persisted entity now contains only the relative file path, you first have to concatenate the configured upload path with the stored filename and create a new File class</p>
  </blockquote>
  
  <p>And it worked.</p>
  
  <p>But on the form's display, the file field says "No file selected"</p>
  
  <p>Here is my controller :</p>
  
  <pre><code>public function editAction(Request $request, Produits $entity)
      {
          $entity-&gt;setPhoto(
              new File($this-&gt;getParameter('images_directory').'/'.$entity-&gt;getPhoto())
          );
          $form = $this-&gt;createForm('ProjectBundle\Form\Produit\ProduitType', $entity);
  
          $form-&gt;handleRequest($request);
          if ($form-&gt;isSubmitted()) {
              if ($form-&gt;isValid()) {
                  $em = $this-&gt;getDoctrine()-&gt;getManager();
                  $em-&gt;persist($entity);
                  $em-&gt;flush();
  
                  $this-&gt;addFlash('success', 'Le produit "'.$entity.'" a été modifié.');
  
                  return $this-&gt;redirectToRoute('produit_show', array('id' =&gt; $entity-&gt;getId()));
              }
          } elseif ($form-&gt;isSubmitted()) {
              $this-&gt;addFlash('error', 'Le produit "'.$entity.'" n\'a pas pu être modifié.');
          }
  
          return $this-&gt;render('ProjectBundle:admin/Produit:edit.html.twig', array(
              'entity' =&gt; $entity,
              'form' =&gt; $form-&gt;createView(),
          ));
      }
  </code></pre>
  
  <p>And in my view :</p>
  
  <pre><code>&lt;div class="input-field{% if form.photo.vars.errors|length %} has-error{% endif %}"&gt;
      {{ form_widget(form.photo,{'attr': {'class': 'form-control'}}) }}
      {{ form_errors(form.photo) }}
  &lt;/div&gt;
  </code></pre>
  
  <p>If I do a <code>{{ dump(form.photo) }}</code> I get all information about the photo belonging to my entity.</p>
  
  <p>Do you have an idea to get the name of the image in the field ?</p>
  
  <p>Thanks !</p>