tor-netdoc: Fix signature of hash_slice_for_verification (pre-fmt)

        /// `None` if the value wasn't computed.

        /// That shouldn't happen.

        // XXXX make no longer pub(crate)

        pub(crate) fn hash_slice_for_verification(&self, algo: $ttype) -> Option<&[u8]> {

        pub(crate) fn hash_slice_for_verification(

            &self,

            algo: $ttype,

        ) -> Option<&[u8]> {

            // XXXX handle sha1_unnamed correctly

            match algo { $(

                $vtype => Some(self.$FNAME.as_ref()?),