Save on scene has changed popup crashes Unity.

1. What happened
Selecting "Dont Save" or "Save" in the "Scene has changed" pop-up menu crashes Unity.

2. How we can reproduce it using the example you attached
- Create a new project in Unity 2018.3.0a8
- Add a Canvas game object to the scene.
- Add an empty game object to the canvas
- In the inspector add a horizontal layout group
- Pop up will appear select "Don't Save" or "Save"
NOTICE ISSUE >> CRASH

NOTE: Pressing "Save" will cause the crash but it will also save Unity in a state where you cannot reproduce the issue. Best to stick with "Don't Save" when repoing as above.

Broken: 2018.3.0a8
Working: 2018.2.1f1, 2018.3.0a6