Ticket 50396 - Crash in PAM plugin when user does not exist
Description: pam passthru & addn plugin causes crash in bind when
user does not exist. Need to make sure we don't
dereference NULL pointer.
https://pagure.io/389-ds-base/issue/50396
Reviewed by: mreynolds & tbordaz
(cherry picked from commit 0935b8af6c8925c7a79a0a22103142ef5f7c5960)