Bug 15210 - Novelist throws an error if no ISBN

 Bug 15210 - Novelist throws an error if no ISBN

This patch makes opac-detail.tt check for an ISBN before attempting to load Novelist content and prevents a js error which breaks other code.

To test:
1 - Enable novelist
2 - Add a visible change to OPACUserJS eg: $(document).ready(function() {$("body").css("background-color","pink");});
3 - Load a record with no ISBN
4 - Note you do not see a color change in the body and that there is an error in the console
5 - Apply patch
6 - Reload the record
7 - You should see the color change and no error in the js

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>