Fix legacy upgrade with missing instance
Fix legacy upgrade with missing instance

If the user is trying to upgrade their account and for some reason the
instance has been deleted in the meantime then we simply redirect to the
main listing of instances.

mysociety/popit,mysociety/popit,Sinar/popit,mysociety/popit,Sinar/popit,Sinar/popit,openstate/popit,openstate/popit,mysociety/popit,mysociety/popit,openstate/popit,openstate/popit,Sinar/popit