### 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
current_menu_option = p_option;
	tab_closing_idx = p_tab;
	Node *scene = editor_data.get_edited_scene_root(p_tab);
	if (!scene) {
		_discard_changes();
		return;
	}
	bool unsaved = EditorUndoRedoManager::get_singleton()->is_history_unsaved(editor_data.get_scene_history_id(p_tab));
	if (unsaved) {
		if (get_current_tab() != p_tab) {
			set_current_scene(p_tab);
		}
		String scene_filename = scene->get_scene_file_path();
		if (current_menu_option == RELOAD_CURRENT_PROJECT) {
			save_confirmation->set_ok_button_text(TTR("Save & Reload"));
			save_confirmation->set_text(vformat(TTR("Save changes to '%s' before reloading?"), !scene_filename.is_empty() ? scene_filename : "unsaved scene"));
		} else {
			save_confirmation->set_ok_button_text(TTR("Save & Close"));
			save_confirmation->set_text(vformat(TTR("Save changes to '%s' before closing?"), !scene_filename.is_empty() ? scene_filename : "unsaved scene"));
		}
		save_confirmation->reset_size();
		save_confirmation->popup_centered();
	} else {
		_discard_changes();
	}
	save_editor_layout_delayed();
	_update_scene_tabs();
}
void EditorNode::_scene_tab_hovered(int p_tab) {