### Godot version

4.1 rc3

### System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 30.0.15.1403) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

### Issue description

This™
![image](https://github.com/godotengine/godot/assets/2223172/cb33110f-a5b0-400a-951f-3fa425f05714)

It can still happen, but it's more difficult to trigger.

### Steps to reproduce

1. Create a new scene with a Control node
2. Add Theme to the Control
3. Open Theme Editor
4. Clear the `theme` property in Control
5. Save, with Theme Editor opened
6. Restart

### Minimal reproduction project

N/A
ERR_FAIL_COND(!instantiated_node);
				bool original_node_is_displayed_folded = original_node->is_displayed_folded();
				bool original_node_scene_instance_load_placeholder = original_node->get_scene_instance_load_placeholder();
				
				instantiated_node->set_name(original_node->get_name());
				
				String original_node_file_path = original_node->get_scene_file_path();
				if (current_edited_scene == original_node) {
					instantiated_node->set_scene_instance_state(original_node->get_scene_instance_state());
					
					if (original_node_file_path.is_empty()) {
						Ref<SceneState> state = current_packed_scene->get_state();
						state->set_path(current_packed_scene->get_path());
						instantiated_node->set_scene_inherited_state(state);
						instantiated_node->set_scene_file_path(String());
					}
					editor_data.set_edited_scene_root(instantiated_node);
					current_edited_scene = instantiated_node;
					if (original_node->is_inside_tree()) {
						SceneTreeDock::get_singleton()->set_edited_scene(current_edited_scene);
						original_node->get_tree()->set_edited_scene_root(instantiated_node);
					}
				}
				
				original_node->replace_by(instantiated_node, false);
				
				original_node->queue_free();
				
				instantiated_node->set_display_folded(original_node_is_displayed_folded);
				instantiated_node->set_scene_instance_load_placeholder(original_node_scene_instance_load_placeholder);