Prevent a leak of QXcbXSettingsPrivate

The private was not deleted. Adding the dtor in turn
causes a warning about not having a virtual dtor
in the base class, so add that as well.

Change-Id: I24a90caf2cf6192a6f17cf5af96b8f77010d9127
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

src/plugins/platforms/xcb/qxcbconnection.h

@@ -324,6 +324,7 @@ private:
 class QXcbWindowEventListener
 {
 public:
+    virtual ~QXcbWindowEventListener() {}
     virtual bool handleGenericEvent(xcb_generic_event_t *, long *) { return false; }
 
     virtual void handleExposeEvent(const xcb_expose_event_t *) {}

src/plugins/platforms/xcb/qxcbxsettings.cpp

@@ -262,6 +262,12 @@ QXcbXSettings::QXcbXSettings(QXcbScreen *screen)
     d_ptr->initialized = true;
 }
 
+QXcbXSettings::~QXcbXSettings()
+{
+    delete d_ptr;
+    d_ptr = 0;
+}
+
 bool QXcbXSettings::initialized() const
 {
     Q_D(const QXcbXSettings);

src/plugins/platforms/xcb/qxcbxsettings.h

@@ -45,6 +45,7 @@ class QXcbXSettings : public QXcbWindowEventListener
     Q_DECLARE_PRIVATE(QXcbXSettings)
 public:
     QXcbXSettings(QXcbScreen *screen);
+    ~QXcbXSettings();
     bool initialized() const;
 
     QVariant setting(const QByteArray &property) const;