Fix getEarliestCreatedFullUser initial value

If user 0 isn't a full admin, its creation time should not be part of the calculation.
Currently, user 0 will generally be the earliest created user, so no other user can get returned (even if user 0 isn't a full user).
This fixes the bug.

Bug: 256624031
Change-Id: Idee2d5957560dd8556c53f85645981816494acc6
Test: local