Bug 11077: remove uninitialized value $pki_field warning

Bug 11077: remove uninitialized value $pki_field warning

During login at the Staff interface you get warnings in the logs
regarding an uninitialized value for the $pki_field variable.

To test:
- tail -f /path/to/your-intranet-logs
- Point your browser to your staff login page
- Login
- Three warnings are showed
- Apply the patch
- Log out
- Log in
- No new warnings, and you can still log in.

Sponsored-by: Universidad Nacional de Cordoba
Signed-off-by: Petter Goksoyr Asen <boutrosboutrosboutros@gmail.com>
Followed test plan; it works as advertised.
Also works when I deleted AllowPKIAuth system pref.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>