Bug 9070: [SIGNED-OFF] authority searches in auth_finder error out

Bug 9070: [SIGNED-OFF] authority searches in auth_finder error out

When using authority records imported into Koha from elsewhere, you
can get an error like:
    Can't use string ("HASH(0xbc6c{30)") as a HASH ref while "strict refs" in use at /usr/share/koha/lib/C4/AuthoritiesMarc.pm line 363.
in authorities/auth_finder.pl. This patch fixes that error.

To test:
1) You will need records imported from elsewhere.
2) Use the authority control plugin in a bib record to search for one of
   those headings.
3) Observe you get a nasty error.
4) Apply patch.
5) Repeat step 2.
6) Observe the error is gone.
7) Sign off.

Signed-off-by: Magnus Enger <magnus@enger.priv.no>
Works as advertised. No warning about "defined(%hash) is deprecated"
under perl v5.10.1.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>