In 49a21155f642670dfea264ac73fb60241f37cb87, I managed to incorrectly
write the `createUnbufferedStream()` function from the AWS SDK as
`getUnbufferedStream()` and to consistently use that naming in the unit
tests.
This commit fixes that. I have tested again on S3.
Document updater 404s are not indicative of a problem, but just of the client
trying to connect to a deleted document, which is easy to trigger. We
log a warning instead.