Bug 14440: get_template_and_user can not have an empty template_name (opac-ratings.pl)

Bug 14440: get_template_and_user can not have an empty template_name (opac-ratings.pl)

Since Bug 14408, the method get_template_and_user can not have an empty template_name.
Pages calling with an empty value should use C4::Auth::checkauth()

This patch corrects opac/opac-ratings.pl

Test plan :
- Apply patch
- Set sysopref OpacStarRatings to 'results and details'
- Disable Javascipt on your browser (otherwise it will use ajax)
- Login at OPAC
- Go to a record
- Click on a button left of 'Rate me' to choose a rating, ie 4
- Click on 'Rate me'
=> The page is reloaded and you see 'your rating: 4'
- Loggout from OPAC
- Try to access URL : http://<serveur>/cgi-bin/koha/opac-ratings.pl
=> You see the loggin page

Signed-off-by: Indranil Das Gupta (L2C2 Technologies) <indradg@gmail.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>