..forth and back..
1882c1ba7edabd5715e9fac8d84786
This needs a [much] better solution:
e.g. Wait until instrument is instantiated (ports are created),
then auto-connect, and finally fan-out
(or alternatively skip auto-connect for fanned-out tracks).
Currently both auto-connect as well as fan-out and port-creation
take place asynchronously.
Also MIDI track subscribe to &Session::midi_output_change_handler,
(MIDI busses don't).