Steps to reproduce:

1. Create new Unity project
2. If you are logged in, log out of your Unity ID
3. Open Services window and make sure it's visible
4. Click 'Log In' to open the login window
5. Close login the window before it's completely loaded
6. CMD+Q to quit Unity Editor right after
7. Editor crashes (note that it doesn't happen 100% of the time, so you might need to do repeat steps 2-6)

Notes:
If you quit editor with only the Login window visible (services window closed) - editor wont crash.
If you quit editor when the Login window finishes loading - editor wont crash.
Likely macOS High Sierra 910.13) specific, couldn't reproduce on a similar machine with macOS 10.12.5

Reproduced with: 2017.3.0b8, 2017.3.0b9
Not reproducible with: 2017.3.0b6, 2018.1.0a3