D5772: hg: raise Abort on invalid path

[Yuya Nishihara]

> +    try:
> +        isfile = os.path.isfile(path)
> +    # Python 2 raises TypeError, Python 3 ValueError.
> +    except (TypeError, ValueError) as e:
> +        raise error.Abort(_('invalid path %s: %s') % (
> +            path, pycompat.bytestr(e)))

I don't know if the path is included in the exception message, but it's
probably safer to use `stringutil.forcebytestr(e)` to get around possible
UnicodeError.