### 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;
	}
	if (!p_layout->has_section(EDITOR_NODE_CONFIG_SECTION) ||
			!p_layout->has_section_key(EDITOR_NODE_CONFIG_SECTION, "open_scenes")) {
		return;
	}
	restoring_scenes = true;
	PackedStringArray scenes = p_layout->get_value(EDITOR_NODE_CONFIG_SECTION, "open_scenes");
	for (int i = 0; i < scenes.size(); i++) {
		load_scene(scenes[i]);
	}
	if (p_layout->has_section_key(EDITOR_NODE_CONFIG_SECTION, "current_scene")) {
		String current_scene = p_layout->get_value(EDITOR_NODE_CONFIG_SECTION, "current_scene");
		int current_scene_idx = scenes.find(current_scene);
		set_current_scene(current_scene_idx);
	}
	save_editor_layout_delayed();
	restoring_scenes = false;
}
bool EditorNode::has_scenes_in_session() {