Bug 23526: Don't use encoded question mark in shib_login_url

Bug 23526: Don't use encoded question mark in shib_login_url

To test:
1 - Enable shib
2 - Do a search
3 - Try to login from search
4 - Get an error
5 - Apply patch
6 - Retry

Note: You do have to fully configure shibboleth, you can simply enable it in koha-conf.xml and check the URLs.
Signed-off-by: Matthias Meusburger <matthias.meusburger@biblibre.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit 16aa7d1c8afe249318767a8a023f7dbddb6843ea)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>