copy AU parameters with plugin

fixes AU-plugin transfer function display.

(LADSPA & LV2 do not need this, connect&run pushes the
parameters)

libs/ardour/audio_unit.cc

@@ -455,6 +455,9 @@ AUPlugin::AUPlugin (const AUPlugin& other)
 
 {
 	init ();
+	for (int i = 0; i < descriptors.size(); ++i) {
+		set_parameter (i, other.get_parameter (i));
+	}
 }
 
 AUPlugin::~AUPlugin ()