Do not allow to de/activate a track while the transport is rolling.

roll_delay and latency are only re-calculated when the transport is stopped.
de/activating a track is also not RT-safe.

libs/ardour/route.cc

@@ -3694,6 +3694,10 @@ Route::denormal_protection () const
 void
 Route::set_active (bool yn, void* src)
 {
+	if (_session.transport_rolling()) {
+		return;
+	}
+
 	if (_route_group && src != _route_group && _route_group->is_active() && _route_group->is_route_active()) {
 		_route_group->foreach_route (boost::bind (&Route::set_active, _1, yn, _route_group));
 		return;