Bug 25440: Fix for "CGI::param called in list context" in smart-rules.pl

Bug 25440: Fix for "CGI::param called in list context" in smart-rules.pl

This warning emitted:

CGI::param called in list context from /admin/smart-rules.pl line 262,
this can lead to vulnerabilities. See the warning in "Fetching the value
or values of a single named parameter" at CGI.pm line 412.

Explained here: https://metacpan.org/pod/CGI#Fetching-the-value-or-values-of-a-single-named-parameter

And because all these params are not multi-params, so simple "scalar .."
forcing for CGI->param is the fix. Changes are transparent and same
values should be assigned as before, just no more warnings.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>