### 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
ResourceImporterScene::add_importer(import_obj2);
			Ref<EditorSceneFormatImporterESCN> import_escn;
			import_escn.instantiate();
			ResourceImporterScene::add_importer(import_escn);
		}
		Ref<ResourceImporterBitMap> import_bitmap;
		import_bitmap.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_bitmap);
	}
	{
		Ref<EditorInspectorDefaultPlugin> eidp;
		eidp.instantiate();
		EditorInspector::add_inspector_plugin(eidp);
		Ref<EditorInspectorRootMotionPlugin> rmp;
		rmp.instantiate();
		EditorInspector::add_inspector_plugin(rmp);
		Ref<EditorInspectorVisualShaderModePlugin> smp;
		smp.instantiate();
		EditorInspector::add_inspector_plugin(smp);
	}
	editor_selection = memnew(EditorSelection);
	EditorFileSystem *efs = memnew(EditorFileSystem);
	add_child(efs);
	
	FileDialog::get_icon_func = _file_dialog_get_icon;
	FileDialog::register_func = _file_dialog_register;
	FileDialog::unregister_func = _file_dialog_unregister;
	EditorFileDialog::get_icon_func = _file_dialog_get_icon;
	EditorFileDialog::register_func = _editor_file_dialog_register;
	EditorFileDialog::unregister_func = _editor_file_dialog_unregister;