title: Symfony 2 file upload: guessExtension() doesn't work for .docx files
body: <pre><code>public function preUpload()
  {
      if (null !== $this-&gt;file) {
          $this-&gt;path = $this-&gt;file-&gt;guessExtension();
  
      }
  }
  </code></pre>
  
  <p>This doesn't work for .docx files.</p>
  
  <p>I get a file stored under the name "myfile." -> no extension.</p>
  
  <p>How to handle this?</p>