koha: add referer cgi emulation sub

This fixes access to guided_reports

koha/Deichman/Plack/Middleware/App.pm

@@ -71,6 +71,9 @@ sub cgi_subprocess {
                 my ($url) = @_;
                 $headers->{Location} = $url;
             },
+            referer => sub {
+                $headers->{Referer};
+            }
         );
     };
     use warnings;