Re: [PATCH v4] promisor-remote: skip move_to_tail when no-op

>
> Previously, when promisor_remote_move_to_tail() is called for a
> promisor_remote which is currently the final element in promisors, a
> cycle is created in the promisors linked list. This cycle leads to a
> double free later on in promisor_remote_clear() when the final element
> of the promisors list is removed: promisors is set to promisors->next (a
> no-op, as promisors->next == promisors); the previous value of promisors
> is free()'d; then the new value of promisors (which is equal to the
> previous value of promisors) is also free()'d. This double-free error
> was unrecoverable for the user without removing the filter or re-cloning
> the repo and hoping to miss this edge case.
>
> Now, when promisor_remote_move_to_tail() would be a no-op, just do a
> no-op. In cases of promisor_remote_move_to_tail() where r is not already
> at the tail of the list, it works as before.