Bug 20455: Fix sort patrons by date expired

We may need to apply this change for all other occurrences in our
codebase.

Test plan:
- Make sure sample patron data is loaded and you have a patron without a
date expired defined
- Make an empty search for all patrons or another search that gives you
a good amount of results
- Try to sort on the date expired column

=> Without this patch you get
Odd number of elements in anonymous hash
at /home/vagrant/kohaclone/C4/Utils/DataTables/Members.pm line 189.
output_pref is called with 'dateonly' (ref SCALAR), not a DateTime
object

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

C4/Utils/DataTables/Members.pm

@@ -178,7 +178,7 @@ sub search {
 
         if( $patron->{dateexpiry} ) {
             # FIXME We should not format the date here, do it in template-side instead
-            $patron->{dateexpiry} = output_pref( { dt => dt_from_string( $patron->{dateexpiry}, 'iso'), dateonly => 1} );
+            $patron->{dateexpiry} = output_pref( { dt => scalar dt_from_string( $patron->{dateexpiry}, 'iso'), dateonly => 1} );
         } else {
             $patron->{dateexpiry} = '';
         }