OpenMage LTS imports cross-user wishlist item via shared wishlist code, leading to private option disclosure and file-disclosure variant

Magento Long Term Support (LTS) is an unofficial, community-driven project provides an alternative to the Magento Community Edition e-commerce platform with a high level of backward compatibility. Prior to version 20.17.0, the shared wishlist add-to-cart endpoint authorizes access with a public `sharing_code`, but loads the acted-on wishlist item by a separate global `wishlist_item_id` and never verifies that the item belongs to the shared wishlist referenced by that code. This lets an attacker use a valid shared wishlist code for wishlist A and a wishlist item ID belonging to victim wishlist B to import victim item B into the attacker's cart through the shared wishlist flow for wishlist A. Because the victim item's stored `buyRequest` is reused during cart import, the victim's private custom-option data is copied into the attacker's quote. If the product uses a file custom option, this can be elevated to cross-user file disclosure because the imported file metadata is preserved and the download endpoint is not ownership-bound. Version 20.17.0 patches the issue.