Invalid Track Alias/Subscribe ID are a protocol violation

[afrind]

Fixes: #458

[martinduke]

The lack of normative language is telling here. Killing a session because a subscriber has set its timer too short ("recently closed") is overkill and can lead to failures.

If the intent is to throw an error when there has not been a SUBSCRIBE or FETCH at all, then write that. If it's to throw an error when a SUBSCRIBE or FETCH has never been opened, then say the Sender MUST NOT do that, and the receiver SHOULD do a protocol error if it has the ability to detect that.

If it's to strictly ban the sending of data for any SUBSCRIBE/FETCH that has closed, it can be a MUST NOT for the sender, but I don't see how you can enforce that at the receiver except to reset the stream, because data can arrive arbitrarily late.