Steps to reproduce :

- create a new project
- open the Asset Store and download the UI Pack : Nightmare https://www.assetstore.unity3d.com/en/#!/content/49146
- open the scene and select Maximize Game View
- play the scene and Unity will crash

*Notes:

I managed to reproduce this crash is two other different ways but not 100% repro tough the same call stack :

- create a new project then switch the layout to default
- create a new project then quit Unity

This seems to be a regression from 5.6.