The Auditioner is not part of the session route-list and the
auditioner route's I/O latency is never updated.
Session::process_audition() does not handle pre-roll either,
so it need to be zeroed, otherwise Route::roll skips samples.
This has lead to initial samples being skipped, IFF the
auditioner's output-port had non-zero latency.
Since private port-latencies are usually only set for routes
in the route-list, and _remaining_latency_preroll is reset
at transport-stop, this *usually* worked...
Last but not least, MIDI notes need to be resolved when seeking.
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