QmlDesigner: Optimize assign operator in resize controller

Change-Id: I6b832cd436a70d4c6976fc192e0b2ad9a6964614
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/plugins/qmldesigner/components/formeditor/resizecontroller.cpp

@@ -164,6 +164,7 @@ ResizeController::~ResizeController()
 
 ResizeController &ResizeController::operator =(const ResizeController &other)
 {
+    if (m_data != other.m_data)
         m_data = other.m_data;
 
     return *this;