Do not leak Downloader-related objects.

Do not leak Downloader-related objects.

The downloadFinished() method was responsible for the job clean up, but
that asynchronous method is not called when the Downloader job quits
before the call can be fired. This early termination happens when, for
example, the job finishes while still inside the start() method (e.g., a
memory hit with no async ACLs to check). It also happens if an exception
is thrown while the job is running under async call protections.

Ensure the cleanup happens regardless of the job path to finish.

This is a Measurement Factory project.