subscription APIs should work in disconnect mode

[ghost]

Currently call get_packet(id) in disconnect mode just freezes the script. Pressing Go has no effect. Ideally we could return an empty packet that was subscribed to because subsequent calls will probably be reading that packet. At the very least, Go should skip past the line.

I think this applies even if you're not in disconnect mode. Go and wait don't work at all and Stop has to do a hard kill.