When exporting many ranges, locate and restarting transport for
every ranged a SessionEvent::TransportStateChange event is queued.
Since freewheel export does not process events. Those events
can accumulate:
https://discourse.ardour.org/t/pipewire-jack-export-freeze/107383/18?u=x42
During export those requests can be safely ignored because the only
purpose is to emit a TransportStateChange() signal when the playhead
passes a given location and notify the UI.