Bug 27861: Warning in C4/XSLT.pm - use of uninitialized value in numeric eq (==)

Bug 27861: Warning in C4/XSLT.pm - use of uninitialized value in numeric eq (==)

In C4/XSLT.pm :
 elsif ( exists $itemtypes->{ $item->effective_itemtype }
            && $itemtypes->{ $item->effective_itemtype }->{notforloan} == 1 )

itemtype.notforloan is null by default, its generated a warning in logs.

Test plan :
1) Choose a record with itemtype.notforloan = NULL
2) Perform a search in the OPAC which will return results which
   include the record using XSLT
3) See patch removed warning

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>