### 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)

}
	if (current != p_state_machine->start_node && p_next.switch_mode == AnimationNodeStateMachineTransition::SWITCH_MODE_AT_END) {
		return pos_current >= len_current - p_next.xfade;
	}
	return true;
}
Ref<AnimationNodeStateMachineTransition> AnimationNodeStateMachinePlayback::_check_group_transition(AnimationTree *p_tree, AnimationNodeStateMachine *p_state_machine, const AnimationNodeStateMachine::Transition &p_transition, Ref<AnimationNodeStateMachine> &r_state_machine, bool &r_bypass) const {
	Ref<AnimationNodeStateMachineTransition> temp_transition;
	Ref<AnimationNodeStateMachinePlayback> parent_playback;
	if (r_state_machine->get_state_machine_type() == AnimationNodeStateMachine::STATE_MACHINE_TYPE_GROUPED) {
		if (p_transition.from == "Start") {
			parent_playback = _get_parent_playback(p_tree);
			if (parent_playback.is_valid()) {
				r_bypass = true;
				temp_transition = parent_playback->_get_group_start_transition();
			}
		} else if (p_transition.to == "End") {
			parent_playback = _get_parent_playback(p_tree);
			if (parent_playback.is_valid()) {
				temp_transition = parent_playback->_get_group_end_transition();
			}
		}
		if (temp_transition.is_valid()) {
			r_state_machine = _get_parent_state_machine(p_tree);
			return temp_transition;
		}
	}
	return p_transition.transition;
}
AnimationNodeStateMachinePlayback::NextInfo AnimationNodeStateMachinePlayback::_find_next(AnimationTree *p_tree, AnimationNodeStateMachine *p_state_machine) const {