Also fix a somewhat related printing bug in the process where
some paths would print "Success." inconsistently even
when there otherwise was no output (in the EditPrefs path)
Fixes#3830
Updates #3702 (which broke it once while trying to fix it)
Change-Id: Ic51e14526ad75be61ba00084670aa6a98221daa5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>