Editor crashes on selecting "Close" or "Don't Save" button from "Save Asset" popup. Save popup appears if "Verify Saving Asset" from Preferences is checked.

Steps to reproduce:
1. Create a new project.
2. Make sure that "Verify Saving Asset" is checked from Unity > Preferences > General
3. Make some changes in Hierarchy Tab. (eg. create or destroy any Gameobject)
4. Unity > Quit
5. Select "Save" from "Scene(s) Have Been Modified"
6. Save asset popup will appear, Select "Close" or "Don't Save"

Actual Result:
Editor crashes

Expected Result:
Editor should quit gracefully without saving changes made.

Reproducible with:
Unity 2018.2.0b1, 2018.2.0a8 , 2018.2.0a1

Working with:
Unity 2018.1.0f1, 2018.1.0b13, 2017.3.0f3

Environment:
Only on Mac 10.12, 10.13