fix request start position for chunks larger than 31952 bytes

[jeffrson]

This PR fixes the later issue in #1162

[mscdex]

This needs a test

[jeffrson]

Done. Test should fail with current master.

[jeffrson]

@mscdex Have you had a look at this rather simple PR? It's a pity it isn't included in the new release, since the fix is rather important for chunks larger than 31952 bytes.

[mscdex]

It hasn't been merged yet because I haven't had time to make sure it's the right change in the right place.

[jeffrson]

Without a doubt I understand that time is short - I just wasn't sure if I had to mention you again. Sorry.

Nevertheless I hope you'll soon find time to confirm the fix or have a better. At the moment I have to reference a personal git repo for a fixed version, which is not ideal.

From the test I adjusted you will see, that it will fail for the current "official" version. I think it's not too uncommon to use buffer sizes slightly larger than 31952, which should always cause an error if the returned position is to be used.