Bug 31217: OPAC coce.js is not hiding the coce-coverimg div for single-pixel images

Bug 31217: OPAC coce.js is not hiding the coce-coverimg div for single-pixel images

This is because opac-detail.tt has coce-coverimg as an ID, but OPAC
coce.js targets coce-coverimg as a class.

opac-detail.tt should be changed to have coce-coverimg as a class.

Test plan:
1. Set your system preferences:
- CoceHost = https://coce.mykoha.co.nz
- CoceProviders = Select all
- OpacCoce = Enable

2. Add the ISBN of '9780262336499' to a biblio

3. Open a "Incognito" window in your browser (recommended to use Google
Chrome to test this)

4. View the biblio detail page in the OPAC. Observe a 'Coce image from
Amazon' box loads with a spinner

5. Apply patch and restart services

6. Clear your browser cache

7. Reload the same biblio detail page in the OPAC. Observe no image is
displayed.

8. View another OPAC biblio detail page that does have a successfully
loading coce image and confirm the source of that image is listed: For
example 'Coce image from Amazon.com' is displayed

Sponsored-by: Toi Ohomai Institute of Technology, New Zealand
Signed-off-by: Paul Derscheid <paul.derscheid@lmscloud.de>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>