Bug 21503: Fix AV to fail to other values

Bug 21503: Fix AV to fail to other values

To Test (Test both detail.pl and opac-detail.pl for functionality):
    1) Apply patch (restart_all)
    2) Look up an item that has a shelving location with a description
        defined (opac description too).
    3) Remove opac description from shelving location.  Refresh
        opac-detail.pl and note that description fails back to the
        regular description.  Refresh detail.pl and note no change.
    4) Remove regular description from shelving location.  Refresh
        opac-detail.pl and detail.pl.  Note that both default to the
        shelving location code.
    5) Remove the shelving location from the LOC table all together.
        Refresh opac-detail.pl and detail.pl.  Note that both default to
        the requested shelving location code.

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>