Consider returning a TypeError for ``.has_state()`` for state size 0

Currently returns a ValueError with a technically correct but not hugely helpful error message:

```
>>> from dwave.optimization import Model
>>> model = Model()
>>> i = model.integer(3, lower_bound=0, upper_bound=20)
>>> i.has_state()
ValueError: index out of range: 0
```

Would it make sense to capture the ``model.states.size() == 0`` condition and if zero, return a TypeError with an explicit error message?