Palettes based in GtkMenu do not have present() method

There are two different palette widgets in Sugar.
_PaletteMenuWidget is a Gtk.Menu and  _PaletteWindowWidget is a Gtk.Window.
Only the palettes where the widget is a Gtk.Window can do present()

src/sugar3/graphics/palette.py

@@ -189,6 +189,7 @@ class Palette(PaletteWindow):
 
     def __map_cb(self, *args):
         # Fixes #4463
+        if hasattr(self._widget, 'present'):
             self._widget.present()
 
     def __destroy_cb(self, palette):