`FunOwlImplementation`: `.entities()` and `.axioms()` produced 0 results

I used `FunOwlImplementation` and tried `.entities()` and `.axioms()`, but got empty lists.

**My version:** `oaklib==0.1.23`

I tried some other implementations, e.g. `SparqlImplementation` and `ProntoImplementation`, which returned results from `.entities()` (didn't try `.axioms()` in those cases), but I got empty lists when I tried this:

```python
ontology = FunOwlImplementation(OntologyResource(slug=ontology_path, local=True))
entities = [x for x in ontology.entities()]
entities = [x for x in ontology.axioms()]
```

Start by reproducing the example with FunOwlImplementation, OntologyResource, and the reported oaklib==0.1.23 environment. Compare the behavior of entities() and axioms() with the mentioned SparqlImplementation and ProntoImplementation; done means the FunOwlImplementation calls return the expected results for the loaded ontology instead of empty lists.

Written by the indexing model from the issue text.