### 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
}
						save_confirmation->reset_size();
						save_confirmation->popup_centered();
						break;
					}
					_discard_changes();
					break;
				}
				if (save_each) {
					tab_closing_menu_option = current_menu_option;
					for (int i = 0; i < editor_data.get_edited_scene_count(); i++) {
						tabs_to_close.push_back(editor_data.get_scene_path(i));
					}
					_proceed_closing_scene_tabs();
				} else {
					String unsaved_scenes;
					int i = _next_unsaved_scene(true, 0);
					while (i != -1) {
						unsaved_scenes += "\n            " + editor_data.get_edited_scene_root(i)->get_scene_file_path();
						i = _next_unsaved_scene(true, ++i);
					}
					if (p_option == RELOAD_CURRENT_PROJECT) {
						save_confirmation->set_ok_button_text(TTR("Save & Reload"));
						save_confirmation->set_text(TTR("Save changes to the following scene(s) before reloading?") + unsaved_scenes);
					} else {
						save_confirmation->set_ok_button_text(TTR("Save & Quit"));
						save_confirmation->set_text((p_option == FILE_QUIT ? TTR("Save changes to the following scene(s) before quitting?") : TTR("Save changes to the following scene(s) before opening Project Manager?")) + unsaved_scenes);
					}
					save_confirmation->reset_size();
					save_confirmation->popup_centered();