Warning in rend_service_intro_has_opened isn't scrubbed

In rend_service_intro_has_opened, this warning:

    log_warn(LD_REND, "Unrecognized service ID %s on introduction circuit %u.",
             serviceid, (unsigned)circuit->base_.n_circ_id);

Should use safe_str_client for the service ID. Even if it's unrecognized, it might be a service we used to offer, and the name shouldn't be logged.

Patch to follow.