### 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)

playback->_start(anodesm.ptr());
			}
			ChildStateMachineInfo child_info;
			child_info.playback = playback;
			
			bool child_found_route = true;
			bool is_current_same_state = temp_path[i] == playback->get_current_node();
			if (!is_parent_same_state) {
				
				String child_path = "/" + playback->get_current_node();
				while (true) {
					Ref<AnimationNodeStateMachine> child_anodesm = p_state_machine->find_node_by_path(concatenated + child_path);
					if (!child_anodesm.is_valid() || child_anodesm->get_state_machine_type() != AnimationNodeStateMachine::STATE_MACHINE_TYPE_GROUPED) {
						break;
					}
					Ref<AnimationNodeStateMachinePlayback> child_playback = p_tree->get(base_path + concatenated + child_path + "/playback");
					ERR_FAIL_COND_V(!child_playback.is_valid(), false);
					child_playback->_set_base_path(base_path + concatenated + "/");
					if (p_test_only) {
						child_playback = child_playback->duplicate();
					}
					child_playback->_travel_main("End");
					child_found_route &= child_playback->_travel(p_tree, child_anodesm.ptr(), false, p_test_only);
					child_path += "/" + child_playback->get_current_node();
				}
				
				playback->_start(anodesm.ptr());
			}
			is_parent_same_state = is_current_same_state;
			bool is_deepest_state = i == temp_path.size() - 1;