Downloads the data for jobs that have an associated file, such as a query's results. Called on Jobs
that are the results of a project forecast or truth queries via submit_query(). NB: It is a 404 Not Found
error if this is called on a Job that has no underlying S3 data file, which can happen b/c: 1) 24 hours has
passed (the expiration time) or 2) the Job is not complete and therefore has not saved the data file. For
the latter you may use busy_poll_job() to ensure the job is done.