Re: [PATCH 04/14] combine-diff: use pointer for parent paths

> Commit d76ce4f734 (log,diff-tree: add --combined-all-paths option,
> 2019-02-07) added a "path" field to each combine_diff_parent struct.
> It's defined as a strbuf, but this is overkill. We never manipulate the
> buffer beyond inserting a single string into it.
>
> And in fact there's a small bug: we zero the parent structs, including
> the path strbufs. For the 0th parent, we strbuf_init() the strbuf before
> adding to it. But for subsequent parents, we never do the init. This is
> technically violating the strbuf API, though the code there is resilient
> enough to handle this zero'd state.
>
> This patch switches us to just store an allocated string pointer.
> Zeroing it is enough to properly initialize it there (modulo the usual
> assumption we make that a NULL pointer is all-zeroes).