### Godot version

v4.0.beta17.mono.official [c40020513]

### System information

Window 11, Forward+, GTX 1060

### Issue description

Adding two theme variations in a row result to a  crash.

https://user-images.githubusercontent.com/93253123/217037249-1ce1d56d-beb6-4435-83ad-9f8a07fe0e96.mp4



### Steps to reproduce

1. Create a project.
2. Create a theme.
3. Double click to go in the theme editor.
4. Click on manage items buttons.
5. In the add type field type a name to add a type.
6. type another name to add a second type.
7. Crash.

### Minimal reproduction project

[ThemeVariationCrash.zip](https://github.com/godotengine/godot/files/10665863/ThemeVariationCrash.zip)

StringName current_selected = property_selected;
	int current_focusable = -1;
	if (property_focusable != -1) {
		
		bool restore_focus = false;
		Control *focused = get_viewport() ? get_viewport()->gui_get_focus_owner() : nullptr;
		if (focused) {
			Node *parent = focused->get_parent();
			while (parent) {
				EditorInspector *inspector = Object::cast_to<EditorInspector>(parent);
				if (inspector) {
					restore_focus = inspector == this; 
					break; 
				}
				parent = parent->get_parent();
			}
		}
		if (restore_focus) {