fix for error with rack attack setup where there is no user agent
fix for error with rack attack setup where there is no user agent

nypl-spacetime/nypl-warper,nypl-spacetime/nypl-warper,NYPL/nypl-warper,NYPL/nypl-warper,NYPL/nypl-warper,NYPL/nypl-warper,nypl-spacetime/nypl-warper,nypl-spacetime/nypl-warper