Fix for Application error on production

PT story https://www.pivotaltracker.com/story/show/72973180

Geocoding method was run on every visit to wso, because Devise's sessions controller updates user model with last_ip and etc. on first :user_signed_in? check.

Added a conditional to run geocoding only if the last_ip has changed.
:+1: wanted to do this but kept forgetting!