Scenario filter drops entities when entity alternative has not been given

[soininen]

Consider an entity with entity alternative set for alternative A. In a scenario which contains alternative B but not A, the entity should be visible if its entity class has active_by_default set to true. This is currently not the case: the entity is always hidden.

[soininen]

Dropping a unit test here, ready to be copy-pasted to test_scenario_filter.py demonstrating the bug:

    def test_entity_with_irrelevant_entity_alternative_is_passed(self):
        with TemporaryDirectory() as temp_dir:
            url = "sqlite:///" + str(Path(temp_dir, "db.sqlite"))
            with DatabaseMapping(url, create=True) as db_map:
                self._assert_success(db_map.add_scenario_item(name="Scenario"))
                self._assert_success(db_map.add_entity_class_item(name="Object", active_by_default=True))
                self._assert_success(db_map.add_entity_item(name="cube", entity_class_name="Object"))
                self._assert_success(db_map.add_entity_alternative_item(entity_class_name="Object", entity_byname=("cube",), alternative_name="Base", active=True))
                db_map.commit_session("Add test data")
            with DatabaseMapping(url) as db_map:
                config = scenario_filter_config("Scenario")
                scenario_filter_from_dict(db_map, config)
                entities = db_map.get_entity_items()
                self.assertEqual(len(entities), 1)