I don't think it matters much from a performance standpoint, but it looks like you could just:

```c
git_buf_clear(&buf);
if (git_buf_printf(&buf,
        "Content-Type: application/x-git-%s-request\r\n"
        "Accept: application/x-git-%s-result",
        s->service, s->service) < 0)
    goto on_error;
git__utf8_to_16(ct, MAX_CONTENT_TYPE_LEN, git_buf_cstr(&buf));
 
if (!WinHttpAddRequestHeaders(s->request, ct, (ULONG) -1L,
        WINHTTP_ADDREQ_FLAG_ADD | WINHTTP_ADDREQ_FLAG_REPLACE)) {
    giterr_set(GITERR_OS, "Failed to add a header to the request");
    goto on_error;
}
```

The only reason to do that would be less code since `WinHttpAddRequestHeaders` can take more than one header at a time, but it probably doesn't matter.