D3612: py3: use pycompat.fsencode() to convert tempfile name to bytes

[Yuya Nishihara]

>      bundle = None
>      try:  # guards bundle
> -        bundlepath = "bundle:%s+%s" % (op.repo.root, bundlefile)
> +        bundlepath = "bundle:%s+%s" % (op.repo.root,
> +                                       pycompat.fsencode(bundlefile))

It's probably better to handle this by callers because a filename passed
to a Mercurial function should always be bytes.