Reset current_record before clearing group

(transplanted from 6c8591e020f818a25b62925a3e4eccd4e49a057f)

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

@@ -750,8 +750,8 @@ class Screen(SignalEvent):
         return [x.id for x in self.group if x.id]
 
     def clear(self):
-        self.group.clear()
         self.current_record = None
+        self.group.clear()
 
     def on_change(self, fieldname, attr):
         self.current_record.on_change(fieldname, attr)