Fix critical bug that prevents repo updates after Android updates

We reset the DB when the user updates their Android major version. I don't know why we do this, but it was requested that we do. So far, we did not reset the repo timestamp, so on next repo update, the app tried to apply a diff against that timestamp repo version which usually fails, because there's no data to apply a diff against. Whenever the diff data is incomplete, we consider this as a new object and throw an exception if the diff data is not sufficient to instantiate the object.