auto-update: under an admin policy the first save drops an old-name 'on' choice #51

Minor (related case) from the data-integrity DI-1 r4 lens on #5: #5 (comment)
(the order-of-rename half is #44).

Under an admin policy that names the auto-update setting, the first settings save drops an old-name "on" choice
(the rename runs on load, not where saving reads the existing file). If the policy is later removed, updates end up
off and the user's "on" choice is lost. Rare: needs such a policy plus an old-name file. Fails safe (off).

Fix: run the same rename where saving reads the existing settings file, with a test under such a policy.