The "Create New World" button is enabled even when the world name is empty when the GUI is initialized

The bug

The "Create New World" button is always enabled when the new world GUI is initialized, even if the world name is empty.

How to reproduce

1. Delete world name and the "Create New World" button is disabled
2. Go to "More World Options"
3. Change World type to Superflat
4. Go to "Customize"
5. Click on "Done" and the "Create New World" button is enabled

Alternatively:

1. Delete world name and the "Create New World" button is disabled
2. Resize the window and the "Create New World" button is enabled