Gui: modernize C++11

* use nullptr

src/Gui/SelectionObjectPyImp.cpp

@@ -46,7 +46,7 @@ std::string SelectionObjectPy::representation(void) const
 PyObject* SelectionObjectPy::remove(PyObject * args)
 {
     if (!PyArg_ParseTuple(args, ""))
-        return 0;
+        return nullptr;
     Selection().rmvSelection(getSelectionObjectPtr()->getDocName(),
                              getSelectionObjectPtr()->getFeatName());
     Py_Return;
@@ -56,11 +56,11 @@ PyObject* SelectionObjectPy::isObjectTypeOf(PyObject * args)
 {
     char* type;
     if (!PyArg_ParseTuple(args, "s", &type))
-        return 0;
+        return nullptr;
     Base::Type id = Base::Type::fromName(type);
     if (id.isBad()) {
         PyErr_SetString(PyExc_TypeError, "Not a valid type");
-        return 0;
+        return nullptr;
     }
 
     bool ok = getSelectionObjectPtr()->isObjectTypeOf(id);
@@ -125,7 +125,7 @@ Py::Tuple SelectionObjectPy::getSubObjects(void) const
     std::vector<PyObject *> subObjs;
 
     for(const auto &subname : getSelectionObjectPtr()->getSubNames()) {
-        PyObject *pyObj=0;
+        PyObject *pyObj=nullptr;
         Base::Matrix4D mat;
         obj->getSubObject(subname.c_str(),&pyObj,&mat);
         if(pyObj)
@@ -159,7 +159,7 @@ Py::Tuple SelectionObjectPy::getPickedPoints(void) const
 
 PyObject *SelectionObjectPy::getCustomAttributes(const char* /*attr*/) const
 {
-    return 0;
+    return nullptr;
 }
 
 int SelectionObjectPy::setCustomAttributes(const char* /*attr*/, PyObject* /*obj*/)