### 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)

deletable_properties = p_enabled;
}
void EditorInspector::_page_change_request(int p_new_page, const StringName &p_array_prefix) {
	int prev_page = per_array_page.has(p_array_prefix) ? per_array_page[p_array_prefix] : 0;
	int new_page = MAX(0, p_new_page);
	if (new_page != prev_page) {
		per_array_page[p_array_prefix] = new_page;
		update_tree_pending = true;
	}
}
void EditorInspector::_edit_request_change(Object *p_object, const String &p_property) {
	if (object != p_object) { 
		return;
	}
	if (changing) {
		return;
	}
	if (p_property.is_empty()) {
		update_tree_pending = true;
	} else {
		pending.insert(p_property);
	}
}
void EditorInspector::_edit_set(const String &p_name, const Variant &p_value, bool p_refresh_all, const String &p_changed_field) {