Fix initial position of variable chooser.

It was showing up 'somewhere' depending on platform.

Task-number: QTCREATORBUG-4270
Reviewed-by: Robert Loehning

src/plugins/coreplugin/variablechooser.h

@@ -64,6 +64,7 @@ private slots:
     void updateCurrentEditor(QWidget *old, QWidget *widget);
     void handleItemActivated(QListWidgetItem *item);
     void insertVariable(const QString &variable);
+    void updatePositionAndShow();
 
 private:
     void createIconButton();