Do a better job flipping the is_sealed flag on PACER Fetch requests

[mlissner]

A client is asking if the Fetch API could handle the is_sealed flag more consistently. My impression is that it doesn't currently set that flag when people try to get documents, but it should, and when it does, the download should be marked as successful.

I think we should investigate this a bit and see if we can do a better job here.