Crash occurs when creating a Prefab then changing the Root component to a Canvas

[Evildea]

Issue description:
Crash occurs when creating a Prefab then changing the Root component to a Canvas, deleting the root, then saving.

Steps to reproduce:

1. Create a Prefab
2. Add a Gui Canvas
3. Press Save
4. Set the Canvas as the root
5. Delete the root
6. Press Save
7. Experience Crash

Please see this video of steps taken: https://drive.google.com/file/d/1WuzzkXjJIIVgh_h-6BT9AZP4wTjI2UAg/view?usp=sharing
Logs are here: Log.txt
No memory dump files were created.

Flax version:
Current Branch 1.1

[mafiesto4]

Fixed in 793bb50 (and in some other commits in the past).