Terminate if pulseaudio recording fails

[chatziko]

#53 fixed the issue that pulseaudio recording got stuck when is_running is false.

But a similar issue remains: if pulseaudio recording itself breaks (eg pulseaudio is restarted), record_pulseaudio waits for chunks that never arrive. This PR fixes this, a chunk with ts == 0 signals record_pulseaudio to exit, and also mic_task_entry fails if recording stops while still running.