Prevent call to display on the _group_changed trigger when there is a parent.

If there is a parent then the call to display will have been taken into account
by the custom signal system included in tryton.

review606002

tryton/gui/window/view_form/screen/screen.py

@@ -244,7 +244,8 @@ class Screen(SignalEvent):
         self.signal('record-modified')
 
     def _group_changed(self, group, record):
-        self.display()
+        if not self.parent:
+            self.display()
 
     def __get_current_record(self):
         if (self.__current_record is not None