title: QCombobox overlaps other widgets when added a new item
body: <p>I see this wierd behavoir happening with QComboBox, it doesn't update as soon as its contents change. To demonstrate the issue here is a sample code and some screen shots.</p>
  
  <p>Initial widget
  <img src="https://i.stack.imgur.com/ooMTq.jpg" alt="enter image description here"></p>
  
  <p>Add Item to combobox <img src="https://i.stack.imgur.com/AMjDe.jpg" alt="enter image description here"> (See how the checkbox is overlapped)</p>
  
  <p>Manually resized updates and adjusts the layout &amp; combobox<img src="https://i.stack.imgur.com/a1Pnd.jpg" alt="enter image description here"></p>
  
  <pre><code>#include &lt;QApplication&gt;
  #include &lt;QtGui&gt;
  
  int main(int argc, char* argv[])
  {
      QApplication app(argc, argv);
  
      QWidget parentWidget;
      QCheckBox checker;
      QComboBox comber;
      QHBoxLayout layoot;
  
      comber.setEditable (true);
      comber.setSizeAdjustPolicy(QComboBox::AdjustToContents);
  
      layoot.addWidget (&amp;comber);
      layoot.addWidget (&amp;checker);
      parentWidget.setLayout(&amp;layoot);
  
      parentWidget.show();
      return app.exec();
  }
  </code></pre>
  
  <p>I tried update() and repaint() on the combobox and also the layout after the item is edited but doesn't have any effect.
  Do I really have to manually resize the widget for the combobox to readjust?? Is anyone aware of a fix for this problem?? </p>
  
  <p>Thank you.</p>
  
  <p>CV</p>