fix(OldProcessing): use IAppConfig to get the selected model

[kyteinsky]

resolves #316

This fixes 2 things:

• use the correct fallback model ID
• read as lazy because if it's stored as lazy and read as non-lazy, it will most likely always return an empty string.

[julien-nc]

This fixes 2 things:

• use the correct fallback model ID
• read as lazy because if it's stored as lazy and read as non-lazy, it will most likely always return an empty string.

[kyteinsky]

/backport to stable32

[backportbot]

The backport to stable32 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable32
git pull origin stable32

# Create the new backport branch
git checkout -b backport/318/stable32

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick b414b859

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/318/stable32

Error: Failed to cherry pick commits: error: no cherry-pick or revert in progress
fatal: cherry-pick failed

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[kyteinsky]

/backport 00b9de6 to stable32