title: Qt 5.7 QFileDialog action doesn't work
body: <p>I got filedialog called inside my main window with this code:</p>
  
  <pre><code>QAction *actionWithShortcut = new QAction();
  actionWithShortcut-&gt;setShortcut(Qt::CTRL + Qt::Key_9);
  actionWithShortcut-&gt;setShortcutContext(Qt::ShortcutContext::WidgetWithChildrenShortcut);
  // added this comment to check does it work at list outside filedialog
  // addAction(actionWithShortcut);
  QFileDialog *fd = new QFileDialog(this);
  fd-&gt;addAction(actionWithShortcut);
  connect(actionWithShortcut, &amp;QAction::triggered, fd, &amp;QFileDialog::reject);
  fd-&gt;show();
  </code></pre>
  
  <p>But looks like I can't add any actions to <code>QFileDialog</code> or they are somehow omitted. Any suggestions? 
  Already tried window flags, options and etc. Can't find any solutions.</p>