### 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 (p_error) {
		switch (p_error) {
			case ERR_CANT_OPEN: {
				show_accept(vformat(TTR("Can't open file '%s'. The file could have been moved or deleted."), p_file.get_file()), TTR("OK"));
			} break;
			case ERR_PARSE_ERROR: {
				show_accept(vformat(TTR("Error while parsing file '%s'."), p_file.get_file()), TTR("OK"));
			} break;
			case ERR_FILE_CORRUPT: {
				show_accept(vformat(TTR("Scene file '%s' appears to be invalid/corrupt."), p_file.get_file()), TTR("OK"));
			} break;
			case ERR_FILE_NOT_FOUND: {
				show_accept(vformat(TTR("Missing file '%s' or one its dependencies."), p_file.get_file()), TTR("OK"));
			} break;
			default: {
				show_accept(vformat(TTR("Error while loading file '%s'."), p_file.get_file()), TTR("OK"));
			} break;
		}
	}
}
void EditorNode::_load_editor_plugin_states_from_config(const Ref<ConfigFile> &p_config_file) {