Bug 23482: Fix BakerTaylor cover images on lists

Bug 23482: Fix BakerTaylor cover images on lists

While this needs a username/pass to fully test, it should be possible to
verify the code changes by comparing to opac-results code

To test:
1 - Enable BakerTaylor images
2 - Enter your usernme and password
3 - Do not fill the BookStore URL
4 - Verify OPAC covers are working
5 - Save some times with covers to a public list
6 - Verify they do not display in list
7 - Apply patch
8 - Verify images now work

Signed-off-by: Kelly McElligott <kelly@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>