fix(session): Log when crypto session data is lost

[ChristophWurst]

Summary

I don't know if this ever happens, but logging it wouldn't be a bad idea, I guess?

The code then calls session_regenerate_id(true), which is known to cause lost sessions: https://www.php.net/manual/en/function.session-regenerate-id.php

Ref #24550

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[ChristophWurst]

/backport to stable27

[backportbot-nextcloud]

The backport to stable27 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable27
git pull origin stable27

# Create the new backport branch
git checkout -b fix/foo-stable27

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable27

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[ChristophWurst]

/backport to stable27

[ChristophWurst]

/backport to stable27