wrong default for the user access time in case of external authentications

follow-up to #171117: Regression: users without administer users permission can not access user profiles of users that never logged in

As sun noted in #1079018-9: React upon user logging in the first time the original issue forgot about external authentications. In case of an external authentication the access time defaults to REQUEST_TIME, while else it's not set by default.

Attached patch makes this case consistent with the usual case.
Note: Having this consistency, one can rely upon the last-access time being 0 during the very first login, what allows us to check it to determine the first login without any additional hacks.