### 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
icon->set_texture(gui_base->get_theme_icon(SNAME("Folder"), SNAME("EditorIcons")));
		} else {
			label->set_text(p_paths[i].get_file());
			icon->set_texture(gui_base->get_theme_icon(SNAME("File"), SNAME("EditorIcons")));
		}
		icon->set_stretch_mode(TextureRect::STRETCH_KEEP_CENTERED);
		icon->set_size(Size2(16, 16));
		hbox->add_child(icon);
		hbox->add_child(label);
		vbox->add_child(hbox);
	}
	if (p_paths.size() > num_rows) {
		Label *label = memnew(Label);
		if (has_file && has_folder) {
			label->set_text(vformat(TTR("%d more files or folders"), p_paths.size() - num_rows));
		} else if (has_folder) {
			label->set_text(vformat(TTR("%d more folders"), p_paths.size() - num_rows));
		} else {
			label->set_text(vformat(TTR("%d more files"), p_paths.size() - num_rows));
		}
		vbox->add_child(label);
	}
	p_from->set_drag_preview(vbox); 
	Dictionary drag_data;
	drag_data["type"] = has_folder ? "files_and_dirs" : "files";
	drag_data["files"] = p_paths;
	drag_data["from"] = p_from;
	return drag_data;
}
void EditorNode::add_tool_menu_item(const String &p_name, const Callable &p_callback) {