pam: Fix issue with changed password not unlocking keyring

If a user (needs to) change their password while authenticating (via
GDM for example), and pam_gnome_keyring is configured to start the
daemon from the session PAM stage, then we were failing to pass the
changed password to our session handler.

Fix this issue so that this workflow works.

https://bugzilla.gnome.org/show_bug.cgi?id=726196