avm1: Fix `SuperObject::get_local_stored`

It should return `None` in order to continue further walking on the
prototype chain.

core/src/avm1/object/super_object.rs

@@ -51,7 +51,7 @@ impl<'gc> TObject<'gc> for SuperObject<'gc> {
         _name: impl Into<AvmString<'gc>>,
         _activation: &mut Activation<'_, 'gc, '_>,
     ) -> Option<Value<'gc>> {
-        Some(Value::Undefined)
+        None
     }
 
     fn set_local(