Bug 11077: Correct more warnings in C4/Auth.pm

Bug 11077: Correct more warnings in C4/Auth.pm

This gets rid of some more warnings.

It also corrects a noisy ne condition.
    $userid = $retuserid if ( $retuserid ne '');
became
    $userid = $retuserid if ( $retuserid );

It also integrates Srdjan Jankovic's patch with Petter Goksoyrsen's
patch, while correcting the problems found.

This includes:
    my $q_userid = $query->param('userid') // '';
along with:
    my $s_userid = '';
and:
    my $s_userid = $session->param('id') // '';
Indentation does not reflect actual scoping.

A missing system preference would have triggered a ubiquitous
undef compare check failure message. This makes the flooding
message more useful, so as to help correct it.
The change to accomplish this was:
        my $pki_field = C4::Context->preference('AllowPKIAuth');
        if (!defined($pki_field)) {
            print STDERR "Error: Missing AllowPKIAuth System Preference!\n";
            $pki_field = 'None';
        }

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit a0b00e4c8bd75a0557e487520fff5e2e39e10803)
Signed-off-by: Fridolin SOMERS <fridolin.somers@biblibre.com>