midiInReset triggers the sysex callback to tell the application that it has
finished with the buffer. Calling midiInAddBuffer results in an infinite loop
so just return during shutdown.
This replaces using ARDOUR_UI::disconnect_from_session which is only used by the
EngineControl class. ARDOUR_UI::disconnect_from_session also disconnects from
the AudioEngine::Halted signal which seems unnecessary as Halted is not emitted
when stopping the engine and calling update_sample_rate() which is already
handled when the AudioEngine::Stopped signal is emitted.
Currently the last backend error string is only set when calling
AudioBackend::start. Errors that occur when calling other AudioBackend methods
like AudioBackend::set_buffer_size do not set the last backend error string.
So until all the required AudioBackend methods return an ErrorCode and
last_backend_error() can be removed just set it to a default string.
Until all errors that occur are correctly indicated by returning an error code
there will still be situations where last_backend_error() is not indicative of
the true error. For instance AudioEngine::start is called and it fails but
returns a valid error code so last_backend_error() is set, then some other
engine/backend method is called that fails and as last_backend_error is not
set the GUI will display the incorrect error message.
* solo groups
* cancel-solo
* SIP <> AFL/PFL changes
The optimized plural-form route_solo_changed() relied on the false
premise that solo-groups and port-connections are disjoint sets.
-=-
e.g. "cancel all solo" calls set_solo(get_routes(), false);
Since All routes are affected, the "non_solo_change" set is empty, and
no changes were propagated up/downstream.
Routes that indirectly change state as group-members, wrongly end up in
the "non_solo_change" list instead of the "solo_change" list.
If a route feeds another in the same group, no changes were propagated.
