### 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
for (int i = 0; i < extensions.size(); i++) {
				file->add_filter("*." + extensions[i], extensions[i].to_upper());
			}
			Node *scene = editor_data.get_edited_scene_root();
			if (scene) {
				file->set_current_path(scene->get_scene_file_path());
			};
			file->set_title(p_option == FILE_OPEN_SCENE ? TTR("Open Scene") : TTR("Open Base Scene"));
			file->popup_file_dialog();
		} break;
		case FILE_QUICK_OPEN: {
			quick_open->popup_dialog("Resource", true);
			quick_open->set_title(TTR("Quick Open..."));
		} break;
		case FILE_QUICK_OPEN_SCENE: {
			quick_open->popup_dialog("PackedScene", true);
			quick_open->set_title(TTR("Quick Open Scene..."));
		} break;
		case FILE_QUICK_OPEN_SCRIPT: {
			quick_open->popup_dialog("Script", true);
			quick_open->set_title(TTR("Quick Open Script..."));
		} break;
		case FILE_OPEN_PREV: {
			if (previous_scenes.is_empty()) {
				break;
			}
			opening_prev = true;
			open_request(previous_scenes.back()->get());
			previous_scenes.pop_back();
		} break;