Reproduction steps:
1. Open the attached project "New Unity Project 9.zip";
2. Observe the crash (sometimes it happens when you double-click on the scene).

Note: Editor crashes only if ShadowTextureRenderer.cs is added to project assets. This script is from Dynamic Shadow Projector: https://www.assetstore.unity3d.com/en/#!/content/35558

Reproduced on: 5.6.0b5.
Not reproduced: 5.5.1p2, 5.4.2p2.
Regression firstly occurred: 5.6.0a1.