Don't do DNS lookup for is_valid_url if there are no IPs to validate against
Don't do DNS lookup for is_valid_url if there are no IPs to validate against

Refs: GH-2665

fotinakis/sentry,BuildingLink/sentry,mitsuhiko/sentry,beeftornado/sentry,mvaled/sentry,daevaorn/sentry,BuildingLink/sentry,daevaorn/sentry,ifduyue/sentry,mvaled/sentry,zenefits/sentry,jean/sentry,beeftornado/sentry,jean/sentry,gencer/sentry,mvaled/sentry,looker/sentry,JamesMura/sentry,nicholasserra/sentry,looker/sentry,jean/sentry,gencer/sentry,JackDanger/sentry,daevaorn/sentry,zenefits/sentry,jean/sentry,mvaled/sentry,looker/sentry,fotinakis/sentry,fotinakis/sentry,BuildingLink/sentry,JackDanger/sentry,mvaled/sentry,beeftornado/sentry,nicholasserra/sentry,ifduyue/sentry,zenefits/sentry,alexm92/sentry,JamesMura/sentry,looker/sentry,daevaorn/sentry,mitsuhiko/sentry,alexm92/sentry,zenefits/sentry,ifduyue/sentry,ifduyue/sentry,mvaled/sentry,gencer/sentry,zenefits/sentry,JackDanger/sentry,JamesMura/sentry,ifduyue/sentry,looker/sentry,BuildingLink/sentry,gencer/sentry,fotinakis/sentry,nicholasserra/sentry,gencer/sentry,jean/sentry,alexm92/sentry,JamesMura/sentry,BuildingLink/sentry,JamesMura/sentry