Bug 8447: Make sure we have enough subfields for broader_headings

Bug 8447: Make sure we have enough subfields for broader_headings

Thanks to wajasu for providing the debugging information, as I cannot
seem to duplicate the problem, even seeing where it could come from.

Fix corrects cases where upon save, a software error complaing about
indicators being wrong as a side effect of a poorly autogenerated
biblio/authority record.

Behvior with this fix causes existing bilio data to to be preserved
while linking to the authority via subtag 9.

Signed-off-by: wajasu <matted-34813@mypacks.net>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>