Locking the difficulty of a world doesn't immediately disable the difficulty button

When locking the difficulty of a world in the World Options screen, the difficulty button isn’t disabled immediately, meaning the difficulty can be changed after locking it. This goes against what is said in the warning screen that appears when locking it.

Steps to reproduce:

1. Open the World Options screen

2. Lock the difficulty

3. Notice how you can still change the difficulty

Expected result:

The difficulty button should be disabled immediately upon locking the difficulty.

Observed result:

The button is not disabled immediately, meaning you can change the difficulty after it has been locked.