Gui: modernize C++: use range-based for loop

src/Gui/View3DPy.cpp

@@ -236,8 +236,8 @@ View3DInventorPy::View3DInventorPy(View3DInventor *vi)
 View3DInventorPy::~View3DInventorPy()
 {
     Base::PyGILStateLocker lock;
-    for (std::list<PyObject*>::iterator it = callbacks.begin(); it != callbacks.end(); ++it)
-        Py_DECREF(*it);
+    for (auto it : callbacks)
+        Py_DECREF(it);
 }
 
 View3DInventor* View3DInventorPy::getView3DIventorPtr()