Don't use replica if both database_write_location and database_replica_location are nil
It can happen during the rollout of the data_consistency
feature flag, that some jobs are already scheduled and that database_write_location
or database_replica_location
will not be provided. This can cause us to read from a stale replica that has not caught up with the latest changes.
We should change this behaviour and fall back to the primary database in this case.