### 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_COND_EDMSG(is_grouped, "Grouped AnimationNodeStateMachinePlayback must be handled by parent AnimationNodeStateMachinePlayback. You need to retrieve the parent Root/Nested AnimationNodeStateMachine.");
	ERR_FAIL_COND_EDMSG(String(p_state).contains("/Start") || String(p_state).contains("/End"), "Grouped AnimationNodeStateMachinePlayback doesn't allow to play Start/End directly. Instead, play the prev or next state of group in the parent AnimationNodeStateMachine.");
	_start_main(p_state, p_reset);
}
void AnimationNodeStateMachinePlayback::next() {
	ERR_FAIL_COND_EDMSG(is_grouped, "Grouped AnimationNodeStateMachinePlayback must be handled by parent AnimationNodeStateMachinePlayback. You need to retrieve the parent Root/Nested AnimationNodeStateMachine.");
	_next_main();
}
void AnimationNodeStateMachinePlayback::stop() {
	ERR_FAIL_COND_EDMSG(is_grouped, "Grouped AnimationNodeStateMachinePlayback must be handled by parent AnimationNodeStateMachinePlayback. You need to retrieve the parent Root/Nested AnimationNodeStateMachine.");
	_stop_main();
}
void AnimationNodeStateMachinePlayback::_travel_main(const StringName &p_state, bool p_reset_on_teleport) {
	travel_request = p_state;
	reset_request_on_teleport = p_reset_on_teleport;
	stop_request = false;
}
void AnimationNodeStateMachinePlayback::_start_main(const StringName &p_state, bool p_reset) {
	travel_request = StringName();
	path.clear();
	reset_request = p_reset;
	start_request = p_state;
	stop_request = false;
}
void AnimationNodeStateMachinePlayback::_next_main() {
	next_request = true;
}
void AnimationNodeStateMachinePlayback::_stop_main() {