Handle audio devices changing during a session #108
Description
It's possible, at least on macOS, for the selected audio devices to disappear during an Interlocutor session. The microphone can disappear during a transmission. Currently, this is invisible to the user. The transmission simply stops, because there's no audio feeding the vocoder. But the UI and apparently the internal state still thinks it's transmitting. The PTT_STOP message still comes out when PTT is turned off in the GUI, even though the transmitter hasn't been on.
Interlocutor probably ought to detect when the microphone device has disappeared/failed and ask the user to pick a new one. Somehow.