rendclient.c doesn't set auth_len in INTRODUCE1 sometimes
While working on 6177, I've discovered that when auth_type is REND_NO_AUTH, rend_client_send_introduction() leaves auth_len uninitialized. This worked with the old INTRODUCE2 parsing code in rend_service_introduce(), but doesn't match the spec and broke with my initial rewrite of the parser. I'll make sure my new rend_service_introduce() handles this behavior, but it should still get fixed - it should be a pretty quick fix.