Don't break on '*' when normalizing attributes to send search results

When returning a search result, if we have a schema we ask it to ``find_attrtype`` for each attribute, which raises when it can't find anything.  However if we've asked to return the ``*`` attribute (e.g. all of them) this will break because it's unlikely we'll have a schema entry for ``*`` as it's a special catch all value.  The fix is to avoid ask the schema to ``find_attrtype`` the ``*`` attribute.