RTA: small fixes:

* redraw when removing all routes: clear Legend
* queue draw after changing settings
* prepare for RTA button on mixer-strip

gtk2_ardour/mixer_strip.cc

@@ -534,6 +534,9 @@ MixerStrip::set_route (std::shared_ptr<Route> rt)
 	if (group_button.get_parent()) {
 		bottom_button_table.remove (group_button);
 	}
+	if (rta_button->get_parent()) {
+		rta_button->get_parent()->remove (*rta_button);
+	}
 
 	RouteUI::set_route (rt);
 

gtk2_ardour/rta_manager.cc

@@ -189,6 +189,10 @@ RTAManager::remove (std::shared_ptr<ARDOUR::Route> route)
 {
 	_rta.remove_if ([route] (RTAManager::RTA const& r) { return r.route () == route; });
 	route->gui_changed ("rta", this); /* EMIT SIGNAL */
+
+	if (_rta.empty ()) {
+		SignalReady (); /* EMIT SIGNAL */
+	}
 }
 
 bool

gtk2_ardour/rta_window.cc

@@ -246,6 +246,7 @@ RTAWindow::rta_settings_changed ()
 	_speed_dropdown.set_text (_speed_strings[(int)RTAManager::instance ()->rta_speed ()]);
 	_warp_dropdown.set_text (_warp_strings[(int)RTAManager::instance ()->rta_warp ()]);
 	_xpos.clear ();
+	_darea.queue_draw ();
 }
 
 void