GOAWAY frame is handled incorrectly

Found while testing Apple's APN HTTP/2-based API. The scenario is: using a development SSL certificate I'm connecting to the production server.
Somehow they allow me to connect with such a certificate, but then, before I send any request (and this means before I've created any stream yet) they immediately send me GOAWAY on stream 0, which is allowed by the protocol. Due to incorrect logic in 'handleGOAWAY' I treat this as a PROTOCOL_ERROR and report this as the server sending us something wrong, while it's not.