### 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 (_initializing_plugins) {
		return;
	}
	Vector<String> enabled_addons;
	for (const KeyValue<String, EditorPlugin *> &E : addon_name_to_plugin) {
		enabled_addons.push_back(E.key);
	}
	if (enabled_addons.size() == 0) {
		ProjectSettings::get_singleton()->set("editor_plugins/enabled", Variant());
	} else {
		enabled_addons.sort();
		ProjectSettings::get_singleton()->set("editor_plugins/enabled", enabled_addons);
	}
	project_settings_editor->queue_save();
}
void EditorNode::set_addon_plugin_enabled(const String &p_addon, bool p_enabled, bool p_config_changed) {
	String addon_path = p_addon;
	if (!addon_path.begins_with("res:")) {
		addon_path = "res:addons/" + addon_path + "/plugin.cfg";
	}
	ERR_FAIL_COND(p_enabled && addon_name_to_plugin.has(addon_path));
	ERR_FAIL_COND(!p_enabled && !addon_name_to_plugin.has(addon_path));
	if (!p_enabled) {
		EditorPlugin *addon = addon_name_to_plugin[addon_path];
		remove_editor_plugin(addon, p_config_changed);
		memdelete(addon);
		addon_name_to_plugin.erase(addon_path);
		_update_addon_config();
		return;
	}