lib/model: Fix file size inconsisency due to enc. trailer
Fixes a regression due to PR #8563, while arguable the bug was actually
introduced in a much older PR #7155, but didn't have any bad effects so
far:
We account for the encryption trailer in the db updater routine,
calculating the file-info size there. However there's no guarantee that
the file-info at this point is still the exact same as when it was
written. It was before, but isn't anymore since introducing the new
EncryptedTrailerSize field.
Fix: Adjust the size in the info at the same place where the trailer is
written, i.e. we definitely have the actual size on disk.
6a66aee489