Bug 30972: Don't replace biblio's local cover images when uploading an image's image

Bug 30972: Don't replace biblio's local cover images when uploading an image's image

When attaching a new cover image to an item we should not replace cover
images attached to the bibliographic record if "Replace existing covers"
is ticked.

Test plan:
Attach 1+ image to a bibliographic record
Attach 1 image to an item of this biblio
Attach another image to the item and seect "replace existing covers"
=> Without this patch the images attached to the biblio are removed
=> With this patch applied only the images attached to the image are
removed

Same if you tick the checkbox when attaching an image to the biblio

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>