To reproduce:
1. Create new project
2. Add new game object to hierarchy
3. Create some more game objects to be the first one's children
4. Create prefab from parent game object
5. Delete the prefab asset
6. Delete some child

Actual behavior: Unity crashes
Expected behavior: deleted game object from the hierarchy

Not reproducible with: 5.2.0f3, 5.2.2f1, 5.2.3p3
Reproducible with: 5.1.4p1, 5.3.0b2, 5.3.0f4, 5.4.0a5