Clean up the cached cursors inside the destructor of QCocoaCursor

Change-Id: I4e1222832efa29680b4e658a5c9109641599a2b9
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

src/plugins/platforms/cocoa/qcocoacursor.h

@@ -53,6 +53,7 @@ class QCocoaCursor : public QPlatformCursor
 {
 public:
     QCocoaCursor();
+    ~QCocoaCursor();
 
     virtual void changeCursor(QCursor * widgetCursor, QWindow * widget);
     virtual QPoint pos() const;

src/plugins/platforms/cocoa/qcocoacursor.mm

@@ -48,6 +48,10 @@
 QT_BEGIN_NAMESPACE
 
 QCocoaCursor::QCocoaCursor()
+{
+}
+
+QCocoaCursor::~QCocoaCursor()
 {
     // release cursors
     QHash<Qt::CursorShape, NSCursor *>::const_iterator i = m_cursors.constBegin();