Bug: `start_index` and `end_index` of CustomPage are broken for lazy pagination

[interDist]

This is due to LazyPaginator not implementing the count method. However, logically, these values should be available for the already-fetched page, independently of whether the pagination is lazy or not.

[aropan]

Same problem.

Why is if paginator.count == 0: necessary? LazyPaginator not working because of him. I think this condition is superfluous here.

https://github.com/shtalinberg/django-el-pagination/blob/4273dbfccd46d58a92e90b1b979f88eb8daab064/el_pagination/paginators.py#L13-L21