Use Py_REFCNT instead of ob_refcnt in generated code

- ob_refcnt is not guaranteed to be there

Author: mrbean-bremen

generator/shellimplgenerator.cpp

@@ -137,7 +137,7 @@ void ShellImplGenerator::write(QTextStream &s, const AbstractMetaClass *meta_cla
 
         s << "if (_wrapper) {" << endl;
         s << "  PYTHONQT_GIL_SCOPE" << endl;
-        s << "  if (((PyObject*)_wrapper)->ob_refcnt > 0) {" << endl;
+        s << "  if (Py_REFCNT((PyObject*)_wrapper) > 0) {" << endl;
         s << "    static PyObject* name = PyString_FromString(\"" << fun->name() << "\");" << endl;
         s << "    PyObject* obj = PyBaseObject_Type.tp_getattro((PyObject*)_wrapper, name);" << endl;
         s << "    if (obj) {" << endl;