Invalid node in the animationTree

[fabriceci]

By checking the project, I found there is an invalid node in the AnimationTree, this led to crash my editor, see: godotengine/godot#51889 and godotengine/godot#51890

[TokageItLab]

@fabriceci Thank you for fixing the core, I've been putting off the crash issue because AnimationTree crashes so often when we use it normally, but in this case, it seems that when there are characters with AnimationTree enabled in multiple scenes at the same time, AnimationTree seems to be generating mysterious nodes. Unfortunately, after your fixed core, still it's occurring... but, the fact that it was visualized is a great achievement. Great work!
If you close the main scene of the sample project and then open the Player scene, it should work fine.

[TokageItLab]

Fixed by godotengine/godot#52131