Fix compilation of QML Designer.

Breakage introduced by bb13b8d65e .

Change-Id: Ib3b13167f5ada0e406275cb4ff4dddfedc222345
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

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

@@ -164,7 +164,9 @@ ResizeController::~ResizeController()
 
 ResizeController &ResizeController::operator =(const ResizeController &other)
 {
+    if (this != &other)
         m_data = other.m_data;
+    return *this;
 }