Better Handle Unavailable Assets in Quotes

When a quote is retrieved by either an admin updating it or a customer trying to purchase, if an asset is no longer deemed licensable, a warning message will appear. The quote cannot be sent to a customer or purchased by a customer until the content is removed or updated within the quote.

Previously, if a quote is retrieved and it contains a non-licensable asset, the user is unable to view the quote and is not presented with an informative error message.