Fix work's add-cover carousel

[jimchamp]

Closes #8906

Restores "next" and "previous" page buttons to the work add-cover carousel.

Technical

An input with name carousel-i18n-strings does not exist on the work's add-cover page. This caused an error during instantiation when i18n strings were parsed, preventing the Carousel from being created.

Now, we check for the carousel-i18n-strings input before attempting to parse its value.

Testing

Screenshot

Stakeholders

@seabelis

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 15.95%. Comparing base (9222960) to head (136727a).

Files	Patch %	Lines
...ibrary/plugins/openlibrary/js/carousel/Carousel.js	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8942      +/-   ##
==========================================
- Coverage   15.96%   15.95%   -0.01%     
==========================================
  Files          89       89              
  Lines        4710     4712       +2     
  Branches      821      822       +1     
==========================================
  Hits          752      752              
- Misses       3449     3450       +1     
- Partials      509      510       +1     

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[cdrini]

Lgtm! Tested:

• ✅ https://testing.openlibrary.org/works/OL262421W/The_Adventures_of_Sherlock_Holmes_12_stories/add-cover works
• ✅ Homepage carousels i18n correctly: https://testing.openlibrary.org/?lang=fr

I'm not sure how we might want to best handle this in the long run; it seems a touch funky that the i18n is optional, in terms of what the interface for this component is? But I think we can resolve that if we ever come across this use case again; I reckon it's pretty niche!

[jimchamp]

I'm not sure how we might want to best handle this in the long run; it seems a touch funky that the i18n is optional, in terms of what the interface for this component is? But I think we can resolve that if we ever come across this use case again; I reckon it's pretty niche!

It may be nice if Carousel.js only handled functionality that applies to all carousels, and maybe some BookCarousel subclass could define functionality that applies specifically to carousels of books? Not sure if something like this would be worth the effort unless it was done in support of creating some other novel variety of carousel.

[cdrini]

Yeah that was my thinking exactly; but I agree it seems like a lot of work just to handle this random one-off carousel :P If we find that we hit this issue again with another carousel, seems worth considering though!