Bug 17764: (bug 17556 follow-up) Fix search for logged out users and lost items

Bug 17764: (bug 17556 follow-up) Fix search for logged out users and lost items

If you are non logged-in and you the search result contain lost items,
you will get:
Can't call method "category" on an undefined value at
/home/liz/koha-src/koha/C4/Search.pm line 2091.

This is because bug 17556 assumed that $userenv was not defined when the
user is logged out. Actually it is, with non defined or empty string
values.

Test plan:
Do a search in the opac that would turn up a whole list of results (and
not just that one) with the lost item included.
 => Without this patch you should get an error
 => With this patch applied you should see the search results

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>