lingo: don't crash sorting invoices that have no creation date (#37208)

combo/apps/lingo/models.py

@@ -663,7 +663,8 @@ class Items(CellBase):
             return ctx
         ctx.update({'title': self.title, 'text': self.text})
         items = self.get_invoices(user=context['user'])
-        items.sort(key=lambda i: i.creation_date, reverse=True)
+        none_date = datetime.datetime(1900, 1, 1)  # to avoid None-None comparison errors
+        items.sort(key=lambda i: i.creation_date or none_date, reverse=True)
         ctx.update({'items': items})
         return ctx