### 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
List<StringName> tl;
	theme_base->get_theme()->get_icon_list(SNAME("EditorIcons"), &tl);
	for (const StringName &E : tl) {
		if (!ClassDB::class_exists(E)) {
			continue;
		}
		icon_type_cache[E] = theme_base->get_theme()->get_icon(E, SNAME("EditorIcons"));
	}
}
void EditorNode::_enable_pending_addons() {
	for (uint32_t i = 0; i < pending_addons.size(); i++) {
		set_addon_plugin_enabled(pending_addons[i], true);
	}
	pending_addons.clear();
}
void EditorNode::_file_dialog_register(FileDialog *p_dialog) {