apply Theme > “Show waveform clipping”

fixes http://tracker.ardour.org/view.php?id=5589#c15515

gtk2_ardour/theme_manager.cc

@@ -290,6 +290,8 @@ void
 ThemeManager::on_show_clip_toggled ()
 {
 	ARDOUR_UI::config()->set_show_waveform_clipping (show_clipping_button.get_active());
+	// "show-waveform-clipping" was a session config key
+	ArdourCanvas::WaveView::set_global_show_waveform_clipping (ARDOUR_UI::config()->get_show_waveform_clipping());
 }
 
 void

libs/canvas/wave_view.cc

@@ -1031,6 +1031,6 @@ WaveView::set_global_show_waveform_clipping (bool yn)
 {
 	if (_global_show_waveform_clipping != yn) {
 		_global_show_waveform_clipping = yn;
-		VisualPropertiesChanged (); /* EMIT SIGNAL */
+		ClipLevelChanged ();
 	}
 }