Bug 27548: "use of uninitialized value" warning on branchoverdues.pl

On the beginning we have empty "location" parameter for this form,
but that not taken into account in comparison and undef warning emitted:
"Use of uninitialized value $location in string eq at
/usr/share/koha/intranet/cgi-bin/circ/branchoverdues.pl line 72" in branchoverdues.pl

Fixed by adding pre-check for $location.

To reproduce:
    1) Head over to "Circulation ->Overdues with fines" page. Check
       intranet-error.log where there will be many warnings
       "Use of uninitialized value $location in string eq at /usr/share/koha/intranet/cgi-bin/circ/branchoverdues.pl line 72".
    2) Apply the patch, refresh the "Overdues with fines" page.
    3) Ensure that the new "use of uninitialized value" warnings didn't appear in the console.

Signed-off-by: David Nind <david@davidnind.com>

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

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

circ/branchoverdues.pl

@@ -69,7 +69,7 @@ my ($tag,$subfield) = GetMarcFromKohaField( 'items.location' );
 my $tagslib = &GetMarcStructure(1,'');
 if ($tagslib->{$tag}->{$subfield}->{authorised_value}) {
     my $values= GetAuthorisedValues($tagslib->{$tag}->{$subfield}->{authorised_value});
-    for (@$values) { $_->{selected} = 1 if $location eq $_->{authorised_value} }
+    for (@$values) { $_->{selected} = 1 if defined $location && $location eq $_->{authorised_value} }
     $template->param(locationsloop => $values);
 }
 # now display infos