Description:

Unity editor crashes when user quits/closes unity and selects 'Close' option in the 'Save Assets' popup. The 'Save Assets' pop up appears if the 'Verify Saving Assets' is checked in the 'Preference' option under 'Edit'

Steps To Reproduce:

1. Launch unity.
2. Create a new project.
3. Select 'Edit' in the menu and proceed to Edit -> Preferences.
4. Set the 'Verify Saving Assets' option as checked.
5. Close the editor.
6. Click on the 'close' button in the 'Save Asset' popup appears.
7. Observe that the editor crashes.

Frequency: 9/10

Additional Note :
1. This issue may not occur the first time user closes unity but will occur afterwards..
2. If the 'Verify Saving Assets' option is already checked, the 'Save Assets' popup appears multiple times. One has to select the 'Close' option in order to observe the crash.

Expected Result :
Unity should close gracefully without any crash.

Observed Result :
Unity crashes when user closes the editor and selects the close option on the 'Save Assets' panel.

Bug Reproducible on : Unity 2018.1.0b1, 2018.1.0a7, 2018.1.0a5, 2018.1.0a1, 2017.3.0f1, 2017.2.0f3, 2017.1.2f1, 5.6.0f3

Environment:

Occurs on Windows only