Steps to repro:

1. Download attached project - https://drive.google.com/open?id=1CUYfEctEbmS1aFEk9ElzGiqzlmQz9J5d
2. Open the project and '464-BakedLightingLights-editor' scene;
3. Wait until scene's lighting auto-bakes;
4. In the Hierarchy select 'Quad' gameobject and delete it.

Actual result:
Crash with the empty stacktrace.
Regression introduced in 2018.3.0a1.

Expected result:
Crash doesn't happen after removing gameobject, while Lightmap Preview window is rendered.

Notes:
- Reproducible in 2018.3.0a3, 2018.3.0a2, 2018.3.0a1;
- Not reproducible in 2018.2.0b10, 2018.1.6f1;
- Reproducible only when new Lighting Preview window is rendered.