Bug 11299: (follow-up) Skip fields with no 9 subfields

Bug 11299: (follow-up) Skip fields with no 9 subfields

To test:
1 - Disable the 'thesaurus' for a controlled field like 600a or 650a
2 - Edit a record and put random data in this field
3 - Try to link, get a JS error
4 - Apply patch
5 - Repeat
6 - No more error, field is not linked (as it has no $9 subfield)

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>