push2: fix issue with solo/mute display when entering mix layout

libs/surfaces/push2/buttons.cc

@@ -737,6 +737,8 @@ Push2::button_master ()
 
 	if (_current_layout != track_mix_layout) {
 		set_current_layout (track_mix_layout);
+	} else {
+		set_current_layout (_previous_layout);
 	}
 }
 

libs/surfaces/push2/track_mix.cc

@@ -182,8 +182,6 @@ TrackMixLayout::selection_changed ()
 void
 TrackMixLayout::show ()
 {
-	selection_changed ();
-
 	Push2::ButtonID lower_buttons[] = { Push2::Lower1, Push2::Lower2, Push2::Lower3, Push2::Lower4,
 	                                    Push2::Lower5, Push2::Lower6, Push2::Lower7, Push2::Lower8 };
 
@@ -194,6 +192,8 @@ TrackMixLayout::show ()
 		p2.write (b->state_msg());
 	}
 
+	selection_changed ();
+
 	Container::show ();
 }