Part: modernize C++11

* use nullptr

src/Mod/Part/App/GeometryExtensionPyImp.cpp

@@ -40,7 +40,7 @@ PyObject *GeometryExtensionPy::PyMake(struct _typeobject *, PyObject *, PyObject
     // never create such objects with the constructor
     PyErr_SetString(PyExc_RuntimeError,
         "You cannot create an instance of the abstract class 'GeometryExtension'.");
-    return 0;
+    return nullptr;
 }
 
 // constructor method
@@ -52,17 +52,17 @@ int GeometryExtensionPy::PyInit(PyObject* /*args*/, PyObject* /*kwd*/)
 PyObject* GeometryExtensionPy::copy(PyObject *args)
 {
     if (!PyArg_ParseTuple(args, ""))
-        return NULL;
+        return nullptr;
 
     Part::GeometryExtension* ext = this->getGeometryExtensionPtr();
     PyTypeObject* type = this->GetType();
-    PyObject* cpy = 0;
+    PyObject* cpy = nullptr;
     // let the type object decide
     if (type->tp_new)
-        cpy = type->tp_new(type, this, 0);
+        cpy = type->tp_new(type, this, nullptr);
     if (!cpy) {
         PyErr_SetString(PyExc_TypeError, "failed to create copy of the geometry extension");
-        return 0;
+        return nullptr;
     }
 
     Part::GeometryExtensionPy* extpy = static_cast<Part::GeometryExtensionPy*>(cpy);
@@ -92,7 +92,7 @@ void GeometryExtensionPy::setName(Py::String arg)
 
 PyObject *GeometryExtensionPy::getCustomAttributes(const char* /*attr*/) const
 {
-    return 0;
+    return nullptr;
 }
 
 int GeometryExtensionPy::setCustomAttributes(const char* /*attr*/, PyObject* /*obj*/)