title: downloading files behind javascript button with htmlunit
body: <p>I am trying to download something an attachment behind a javascript button with HtmlUnit. Performing other tasks works great (eg. navigating, login).
  I checked out the attachment unit test but it didnt help me.</p>
  
  <pre><code>final WebClient webClient = new WebClient(BrowserVersion.FIREFOX_24);
  final HtmlPage page1 = webClient.getPage( loginUrl );
  final HtmlTextInput textField =  page1.getElementByName(user);
  final HtmlPasswordInput pwd =  page1.getElementByName(pwd);  
  textField.setValueAttribute(User.getUsername());
  pwd.setValueAttribute(User.getPassword());   
  
  final HtmlSubmitInput button =  page1.getElementByName(login);
  final HtmlPage page2 =  button.click();
  
  String buttonJavaScript = "window.location='"+folder+filename + ....... ";
  ScriptResult result = page2.executeJavaScript(buttonJavaScript);
  webClient.waitForBackgroundJavaScript(2000);    
  
  InputStream is = result.getNewPage().getWebResponse().getContentAsStream();
  try {
      File f = new File("filename.extension");
      OutputStream os = new FileOutputStream(f);
      byte[] bytes = new byte[1024];
      while (read == is.read(bytes)) {
          os.write(bytes, 0, read);
      }
      os.close();
      is.close();
  } catch (IOException ex) {
      // Exception handling
  }
  </code></pre>
  
  <p>However, it stops with:</p>
  
  <pre><code>runtimeError: message=[No node attached to this object] sourceName=[http://pagead2.googlesyndication.com/pagead/osd.js] line=[7] lineSource=[null] lineOffset=[0]
  </code></pre>
  
  <p>The file created is size 0.
  There must be a way to get to the real file attached?!</p>
  
  <p>Thank you in advance</p>