Check for work key before rendering list showcase

[jimchamp]

Closes #8983

Checks for a work key before rendering the work list showcase on book pages.

Technical

On orphaned edition book pages, an IndexError was being thrown by the get_seed_info call in lists/widget.html, here. In these cases, a dummy Work object, which has an empty string as its key, is passed to get_seed_info, which requires a Thing with a non-empty string to function correctly.

Since the dummy work object is truthy, we also have to check for a work.key before rendering the work list showcase.

Testing

1. Visit an orphaned edition's book page. Ensure that there are no error messages rendered on the page ("Lists" section and flash message).
2. Visit a work's book page and a non-orphaned edition's book page. Confirm that these are rendering without error.

Screenshot

Stakeholders

[cdrini]

Lgtm! Confirmed working on:

• orphan https://testing.openlibrary.org/books/OL9259100M/Adventures_in_Reading_Beg_SB
• non-orphan https://testing.openlibrary.org/books/OL28596822M/Organizational_Behavior_Global_Edition
• work https://testing.openlibrary.org/works/OL510735W/Organizational_Behavior?edition=key%3A/books/OL28596822M