x11/swaylock: unbreak PAM locking

Since 1.5 it includes "login" service which doesn't ask for password
from user running Wayland session. Before pam_authenticate(3) failed
with PAM_AUTH_ERR due to missing permissions password database.

PR: 248053
Reported by: many
Submitted by: andrew|_|tao11.riddles.org.uk, jbeich
Tested by: ashish