How to reproduce:
1. Create a new Unity project
2. Import the tester-attached script(Bug.cs)
3. Create a new GameObject and attach the script
4. Create a Prefab from this GameObject
5. If the Editor does not freeze/crash at this point - create more Prefabs from separate GameObjects with this script

Expected result: the Editor does not crash/become unresponsive
Actual result: the Editor crashes/becomes unresponsive

Reproducible with: 2019.1.0a13, 2019.1.8f1, 2019.2.0b7, 2019.3.0a7
Not reproducible with: 2017.4.29f1, 2018.4.3f1, 2019.1.0a12

Notes:
The Editor crashes without freezing or any stack trace on Windows
The Editor freezes on macOS, crashes when closed with 2019.3 versions of Unity
With 2019.1.0a11 and 2019.1.0a12, creating a Prefab from a GameObject with the script does not freeze, but sometimes crashes the Editor