rend_client_any_intro_points_usable leaks an extend_info_t

rend_client_get_random_intro_impl returns a pointer to a newly allocated extend_info_t, which rend_client_any_intro_points_usable drops on the floor.

Introduced in commit 748350ace11fa55758fb8bafe5e5556867dd9c23 (0.2.2.25-alpha), when rend_client_any_intro_points_usable was added.