OSX specific, related to the wxWidgets 3.1.4: Fixed wrong UI-scaling

(wxWidgets 3.1.4 can binding of wxEVT_DPI_CHANGED now, so it was called msw_rescale() for most of the controls redundantly)

+ Fixed update of the DoubleSlider after changing of the system color

src/slic3r/GUI/Plater.cpp

@@ -6209,6 +6209,7 @@ void Plater::msw_rescale()
 
 void Plater::sys_color_changed()
 {
+    p->preview->sys_color_changed();
     p->sidebar->sys_color_changed();
 
     // msw_rescale_menu updates just icons, so use it