Steps to reproduce:

1. Download the attached project (DrArm-TerrainHolesRepro)
2. Open the TerrainRepro scene
3. Generate lighting using either CPU or GPU lightmapper
4. Baking stalls

Notes:

- Reproduces both with CPU and GPU lightmappers; Enlighten baked GI is not affected
- Reproduces in: 2021.2.0a15, 2021.2.0a16, 2021.2.0b1, 2021.2.0b4, 2021.2.12f1, 2022.1.0b8, 2022.2.0a1
- Does not reproduce in: 2021.2.0a4, 2021.2.0a8, 2021.2.0a12, 2021.2.0a14, 2021.1.20f1
- Uncovered while verifying the following issue: https://fogbugz.unity3d.com/f/cases/1384239/

Editor log print:

[PathTracer] Failed to add geometry for terrain with hash '6651e6407e4c7571df7c168c1d1232c8'; terrain has no triangles or is fully covered by hole(s).