Bug 25273: (follow-up) Don't die on unknown authtype

Bug 25273: (follow-up) Don't die on unknown authtype

We are guessing authtype code and inserting the heading built accorindg to C4::Heading

If we can't identify the auth type, we can format the heading. There is a record in the koha test
data that is missing the heading field so type cannot be idenfitied

This prevents us from dying n a record where we cannot identify the type.

Note: This code will also be triggered for custom authority types, higlighting
that they won't link because of hardcoded mappings in C4::Heading. We must tackle this
on a new bug

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