`Range` requests not properly handled anymore

[Travis Ralston]

There's a bit of chicken and egg going on here too. We process the Range request after the request has happened, but not before, meaning things like the download pipeline are always told -1, -1.

Problem is, most range requests from browsers contain a start but no end. We can't ask for more bytes than are available, so we need to know the possible response size before we submit the pipeline call. We don't know what the response size is until the pipeline runs though.

Somehow this needs to work.