Bug 35558: Do not retrieve the local image if none exists

Bug 35558: Do not retrieve the local image if none exists

On the search results we are fetching the thumbnails of the local cover
images using catalogue/image.pl
Which means 1 GET per results on the page.

This patch suggests to have this information beforehand in order to
reduce the number of hits and network traffic?

However the page load will be slightly slower ofc.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>