### Godot version

v4.1.rc2.official [46424488e]

### System information

Godot v4.1.rc2 - Windows 10.0.22621 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3060 (NVIDIA; 31.0.15.3623) - AMD Ryzen 7 5700G with Radeon Graphics (16 Threads)

### Issue description

When setting the AnimationTree to active, Godot crashes.

### Steps to reproduce

https://github.com/godotengine/godot/assets/46705245/dbe5eb81-1357-43e8-ac80-a4eb97eea9fc

### Minimal reproduction project

[Crash.zip](https://github.com/godotengine/godot/files/11945826/Crash.zip)

ERR_FAIL_INDEX_V(p_transition, transitions.size(), Ref<AnimationNodeStateMachineTransition>());
	return transitions[p_transition].transition;
}
StringName AnimationNodeStateMachine::get_transition_from(int p_transition) const {
	ERR_FAIL_INDEX_V(p_transition, transitions.size(), StringName());
	return transitions[p_transition].from;
}
StringName AnimationNodeStateMachine::get_transition_to(int p_transition) const {
	ERR_FAIL_INDEX_V(p_transition, transitions.size(), StringName());
	return transitions[p_transition].to;
}
bool AnimationNodeStateMachine::is_transition_across_group(int p_transition) const {
	ERR_FAIL_INDEX_V(p_transition, transitions.size(), false);
	if (get_state_machine_type() == AnimationNodeStateMachine::STATE_MACHINE_TYPE_GROUPED) {
		if (transitions[p_transition].from == "Start" || transitions[p_transition].to == "End") {
			return true;
		}
	}
	return false;
}
int AnimationNodeStateMachine::get_transition_count() const {