Fix: Fix logic in project.save() for Python 3.11+

[alcrene]

Now all objects define __getstate__ (with default value None)

Previous logic in project.save() would test for existence of that method, and if present, use it to populate a state variable.
This no longer works, because a None value passes the first test (it exists) but it is obviously not callable.
This small patch adds support for Python 3.11+ by also checking that __getstate__ is not None before attempting to call it.