### 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
if (!bool(EDITOR_GET("interface/scene_tabs/restore_scenes_on_load"))) {
		return false;
	}
	Ref<ConfigFile> config;
	config.instantiate();
	Error err = config->load(EditorPaths::get_singleton()->get_project_settings_dir().path_join("editor_layout.cfg"));
	if (err != OK) {
		return false;
	}
	if (!config->has_section(EDITOR_NODE_CONFIG_SECTION) || !config->has_section_key(EDITOR_NODE_CONFIG_SECTION, "open_scenes")) {
		return false;
	}
	Array scenes = config->get_value(EDITOR_NODE_CONFIG_SECTION, "open_scenes");
	return !scenes.is_empty();
}
bool EditorNode::ensure_main_scene(bool p_from_native) {