max recursion depth reached when creating offer with condition range but no condition type

The reason is that `Condition.description` is called on a non-proxy object, which then tries to resolve to the proxy using `proxy()` which falls back to `self`. Then `description` is called on `self` again, completing the circle.

This can be recreated in the admin. The incomplete conditional offer stays in the session until the user logs out and back in again.

Oscar 0.7