Fix `HTTPError.response` comparison.
    
    The `requests.Response` evaluates to `True` if it is `HTTP 200 OK`,
    otherwise it is `False`. The code changes by this commit however
    wanted to check if `e.response` is None or set to some Response.
    This did not work, because even if `e.response` was set, it evaluated
    to `False`, because its status code was `401`.