### 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)

case NOTIFICATION_EXIT_TREE: {
			if (!sub_inspector) {
				get_tree()->disconnect("node_removed", callable_mp(this, &EditorInspector::_node_removed));
			}
			edit(nullptr);
		} break;
		case NOTIFICATION_VISIBILITY_CHANGED: {
			set_process(is_visible_in_tree());
		} break;
		case NOTIFICATION_PROCESS: {
			if (update_scroll_request >= 0) {
				get_v_scroll_bar()->call_deferred(SNAME("set_value"), update_scroll_request);
				update_scroll_request = -1;
			}
			if (update_tree_pending) {
				refresh_countdown = float(EDITOR_GET("docks/property_editor/auto_refresh_interval"));
			} else if (refresh_countdown > 0) {
				refresh_countdown -= get_process_delta_time();
				if (refresh_countdown <= 0) {
					for (const KeyValue<StringName, List<EditorProperty *>> &F : editor_property_map) {
						for (EditorProperty *E : F.value) {
							if (E && !E->is_cache_valid()) {
								E->update_property();
								E->update_editor_property_status();
								E->update_cache();
							}
						}
					}
					refresh_countdown = float(EDITOR_GET("docks/property_editor/auto_refresh_interval"));
				}