There are two checks that need to be performed:
1. the crypto stream must not have any more data queued for reading
2. when receiving CRYPTO frames for that crypto stream afterwards, they
must not exceed the highest offset received on that stream
There are two ways that an error can occur during the handshake:
1. as a return value from qtls.Handshake()
2. when new data is passed to the crypto setup via HandleData()
We need to make sure that the RunHandshake() as well as HandleData()
both return if an error occurs at any step during the handshake.
