Prefabs lose runtime graph reference when deleting and regenerating the runtime graph

Steps to reproduce:

1. Create game object with a behavior graph agent in the scene and assign a behavior graph to it
2. Make a prefab out of the game object
3. Click on the behavior graph asset and press the "Delete Runtime Assets" button
4. Open the graph and close the window to regenerate the runtime assets
5. Click on the game object in the scene and observe the inspector (it gets updated with the new runtime graph)
6. Click on the prefab and observe the inspector

Actual results: The prefab shows a missing reference for the graph

Expected results: The prefab references the runtime graph

Reproducible with versions: 
1.0.8

Tested on (OS): MacOS

Notes:

• Reversing steps 5 and 6, i.e. pressing the prefab first, makes it so that the prefab references the graph correctly