Prerequisites:
The issue reproduces on laptop with GPU having 2GB of VRAM.

Steps to repro:
1. Open attached project and 't1BugTerrainScratch' scene;
2. In the Lighting window press 'Generate Lighting' button.

Expected result:
Lightmapper gracefully falls back to CPU PLM. The baking proceeds and finished successfully.

Actual result:
Editor crashes silently, without stacktrace.

Notes:
- Reproducible in 2019.2.0a2, 2019.1.0b1, 2018.3.3f1;
- Reproducible on Windows 10;
- Reproducible when baking on GeForce 640m; not reproducible when baking on GeForce GTX1070 (8GB VRAM);
- Reproducible when baking 4k terrain; not reproducible when baking 2k terrain.