### 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
for (int i = 0; i < hsplits.size(); i++) {
		p_layout->set_value(p_section, "dock_hsplit_" + itos(i + 1), hsplits[i]->get_split_offset());
	}
	
	p_layout->set_value(p_section, "dock_filesystem_split", FileSystemDock::get_singleton()->get_split_offset());
	p_layout->set_value(p_section, "dock_filesystem_display_mode", FileSystemDock::get_singleton()->get_display_mode());
	p_layout->set_value(p_section, "dock_filesystem_file_sort", FileSystemDock::get_singleton()->get_file_sort());
	p_layout->set_value(p_section, "dock_filesystem_file_list_display_mode", FileSystemDock::get_singleton()->get_file_list_display_mode());
	PackedStringArray selected_files = FileSystemDock::get_singleton()->get_selected_paths();
	p_layout->set_value(p_section, "dock_filesystem_selected_paths", selected_files);
	Vector<String> uncollapsed_paths = FileSystemDock::get_singleton()->get_uncollapsed_paths();
	p_layout->set_value(p_section, "dock_filesystem_uncollapsed_paths", uncollapsed_paths);
}
void EditorNode::_save_open_scenes_to_config(Ref<ConfigFile> p_layout) {
	PackedStringArray scenes;
	for (int i = 0; i < editor_data.get_edited_scene_count(); i++) {
		String path = editor_data.get_scene_path(i);
		if (path.is_empty()) {
			continue;
		}
		scenes.push_back(path);
	}
	p_layout->set_value(EDITOR_NODE_CONFIG_SECTION, "open_scenes", scenes);
	String currently_edited_scene_path = editor_data.get_scene_path(editor_data.get_edited_scene());
	
	if (!currently_edited_scene_path.is_empty()) {
		p_layout->set_value(EDITOR_NODE_CONFIG_SECTION, "current_scene", currently_edited_scene_path);
	}
}
void EditorNode::save_editor_layout_delayed() {