Bug 28314: Spinning icon is not always going away for local covers in staff

Bug 28314: Spinning icon is not always going away for local covers in staff

The spinner is always visible with images which are under 80-90 px high

this patch remove the spinner when the image is loaded.

To test:
1. Make sure the LocalCoverImages system preference is enabled
   1.1. Go to Administration > Global system preferences
   1.2. Search for Coverimages
   1.3. Set LocalCoverImages to 'Show'
   1.4. Click 'Save all Enhanced content preferences'
2. Add a short local cover image to a record (I added one which is just a grey rectangle with the size printed on it, to facilitate the test)
   2.1. Download the attached image
   2.2. Find a record without an image
   2.3. Click the 'Images' tab
   2.4. Click 'Upload'
   2.5. Click 'Drop files here or click to select a file' and choose the downloaded image
   2.6. Click 'Process images'
   2.7. Click on the title of the record in the page heading to access the detailed record
   --> Note that the image is displayed normally, but the spinner is also displayed
4. Apply the patch
5. Search for the previous record with the small image
6. Click on the title of the record in the page heading to access the detailed record
   --> Note that the spinner is no more displayed

Signed-off-by: Andrew Fuerste-Henry <andrewfh@dubcolib.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>