title: QCompleter doesn't work properly with NetworkRequest finished
body: <p>Qcompleter which is associated with a lineEdit doesn't work in the slot of a QNetworkRequest finished.The Qcompleter disappeared quite quickly.Each time the text in lineEdit changed a request was send.I tried a demo without other code,it also occured.</p>
  
  <p>Every time the text in lineEdit was edit,a request contains the text will be send to my server.And then I want to show the content in reply in a Qcompleter.But the prompt disappears in a instant.</p>
  
  <pre class="lang-cpp prettyprint-override"><code>void MainWindow::onRequestFinished(QNetworkReply* reply){
  
      QStringList stringList;
      stringList &lt;&lt; "test1" &lt;&lt;"test2"&lt;&lt;"test3";
      QCompleter* completer = new QCompleter(stringList,this);
      completer-&gt;setCompletionMode(QCompleter::UnfilteredPopupCompletion);
      ui-&gt;lineEdit-&gt;setCompleter(completer);
      reply-&gt;deleteLater();
  }
  
  void MainWindow::on_lineEdit_textChanged(const QString &amp;arg1)
  {
      QUrl url("http://www.google.com");
      QNetworkRequest request;
      request.setUrl(url);
      manager-&gt;get(request);
  }
  
  </code></pre>
  
  <pre class="lang-cpp prettyprint-override"><code>MainWindow::MainWindow(QWidget *parent) :
      QMainWindow(parent),
      ui(new Ui::MainWindow){
  ...
  this-&gt;manager = new QNetworkAccessManager(this);
  connect(manager,SIGNAL(finished(QNetworkReply*)),this,SLOT(onRequestFinished(QNetworkReply*)));
  ...
  }
  </code></pre>