Steps to reproduce:

1. Open attached project.
2. Execute menu item: POPUP/Create scene
3. Execute menu item: POPUP/Replace scene with invalid source
4. Execute menu item: POPUP/Create scene

Editor freezes.

if moving focus away and back again after step 3, unity will delete scene created in step 2, thinking that it's meta file, while it's actually a normal scene. Failed FileUtil.ReplaceFile somehow corrupts it.

Reproduced on 5.6.0a2, 5.5.0b11