Bug 29263: (bug 24387 follow-up) Fix 'Cancel' link when editing a html custom

Bug 29263: (bug 24387 follow-up) Fix 'Cancel' link when editing a html custom

When editing content that is a html customization, the 'cancel' link
should redirect to the html custom list, not the 'news' list.

Test plan:
Create or edit a html customization, click the 'Cancel' link
=> You should be redirected to the html custom list

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>