Opening the "Open World" dialog resets the scene

[navzam]

Clicking World -> Open (even if you don't actually open another world) resets the current scene, making you lose all unsaved changes.

Repro:

1. Create a custom world (or open one if you already have one created)
2. Make any change to the scene, like adding a new item. Do NOT save the world
3. Click World -> Open to open the "Open World" dialog. Do NOT click "Accept"
4. Notice the scene behind the dialog has reset