Update ColorPicker controls when entering tree

(cherry picked from commit 03d4ebf12993c3dc1663cb946687d60ee1be58f0)

scene/gui/color_picker.cpp

@@ -55,6 +55,7 @@ void ColorPicker::_notification(int p_what) {
 			btn_pick->set_icon(get_icon("screen_picker", "ColorPicker"));
 			bt_add_preset->set_icon(get_icon("add_preset"));
 
+			_update_controls();
 			_update_color();
 
 #ifdef TOOLS_ENABLED