Re: [PATCH 05/11] cache-tree: simplify locking logic

> After we have taken the lock using `LOCK_DIE_ON_ERROR`, we know that
> `newfd` is non-negative. So when we check for exactly that property
> before calling `write_locked_index()`, the outcome is guaranteed.
>
> If we write and commit successfully, we set `newfd = -1`, so that we can
> later avoid calling `rollback_lock_file` on an already-committed lock.
> But we might just as well unconditionally call `rollback_lock_file()` --
> it will be a no-op if we have already committed.
>
> All in all, we use `newfd` as a bool and the only benefit we get from it
> is that we can avoid calling a no-op. Remove `newfd` so that we have one
> variable less to reason about.