Bug 18946 - Change language from external web fails

Bug 18946 - Change language from external web fails

How to reproduce:
1. Get a multilingüal Koha like
http://demo1.orex.es/cgi-bin/koha/opac-changelanguage.pl?language=en
http://demo1.orex.es/cgi-bin/koha/opac-changelanguage.pl?language=es-ES

2. Copy that urls to any web page in an other domain -it must be in some
host - and try to link to the spanish or english version,it will keep you in the same position.

3. Apply this patch and try again , everything should work fine .

Signed-off-by: Hugo Agud <hagud@orex.es>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>