* Fix again updateLastSeenUnchanged
https://github.com/FreshRSS/FreshRSS/pull/5382 was not good enough to fix markAsReadUponGone and introduced a regression in `entry.lastSeen`.
New approach.
Follow-up of https://github.com/FreshRSS/FreshRSS/pull/5315
* Minor change of mind
* Fix handling of lastSeen
entry.lastSeen was not always correctly initialised, and sometimes overriden