Bug 23785: Fix call get_coins on undef value in opac-search.pl

Bug 23785: Fix call get_coins on undef value in opac-search.pl

If the search engine index returns a record that is no longer in the DB,
an OPAC search will explode with:
  Can't call method "get_coins" on an undefined value at
  /usr/share/koha/opac/cgi-bin/opac/opac-search.pl line 692.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Joy Nelson <joy@bywatersolutions.com>
(cherry picked from commit 8073350819ea0fa73e3492e62b52575fecaecc3e)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>