Fixup for previous commit - SL #4224

The palette can be None.

Signed-off-by: Manuel Quiñones <manuq@laptop.org>

src/sugar3/graphics/icon.py

@@ -727,7 +727,7 @@ class CanvasIcon(EventIcon):
         self.unset_state_flags(Gtk.StateFlags.PRELIGHT)
 
     def __button_press_event_cb(self, icon, event):
-        if not self.palette.is_up():
+        if self.palette and not self.palette.is_up():
             self.set_state_flags(self.get_state_flags() | Gtk.StateFlags.ACTIVE,
                                  clear=True)