App: Fix ExtensionPython macro

src/App/Extension.cpp

@@ -69,6 +69,7 @@ using namespace App;
 Extension::~Extension()
 {
     if (!ExtensionPythonObject.is(Py::_None())) {
+        Base::PyGILStateLocker lock;
         // Remark: The API of Py::Object has been changed to set whether the wrapper owns the passed
         // Python object or not. In the constructor we forced the wrapper to own the object so we
         // need not to dec'ref the Python object any more. But we must still invalidate the Python