Description
When a BehaviorGraphAgent with no assigned graph is selected in the Inspector, loading a graph from code fails for that GameObject upon entering Play mode.

Steps to Reproduce

1. Create a new GameObject in the scene
2. Add a script and an empty BehaviorGraphAgent (no graph assigned) to the GameObject
3. Duplicate the GameObject
4. Select one of the GameObjects (so the Inspector displays the BehaviorGraphAgent with no graph assigned)
5. Enter Play mode

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Actual results: 
The selected GameObject's BehaviorGraphAgent's graph remains null, while the unselected one loads correctly.

Expected results: 
When entering Play mode, both GameObjects should have their BehaviorGraphAgent's graph properly assigned.

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Reproducible with versions: 
1.0.10, 1.0.11