Clear (invalid) checksum when upgrading from OC

When upgrading from OC 10.5.0 to NC 21.0.0beta2 we should clear the checksums in the database.
As far as I saw any upload from the NC desktop client would also clear the checksum, so we should do it right away or have an occ command to do so.

Why ? Because if there are broken checksums the desktop client will not sync the files.

In my own setup I had some broken checksums on OC before doing the upgrade. How I managed to have broken checksums, not sure... I interrupted a request that was restoring files from trashbin.

Steps (guessed from my setup)

1. Setup OC 10.5.0
2. Upload a bunch of TXT files using the NC desktop client (which means you'll still have a local copy)
3. Edit oc_filecache and manually corrupt the checksum of a file "test-corrupt.txt"
4. Upgrade to NC 21.0.0beta2
5. Run the NC desktop client
6. Edit "test-corrupt.txt" locally
7. Check the server version in the web UI

Expected result

"test-corrupt.txt" can be uploaded, the file is changed on server.

Actual result

"test-corrupt.txt" is not uploaded, the NC desktop client says there's a checksum mismatch.

Versions

OC 10.0.5 -> NC 20.0.0beta2
NC desktop client 3.1.0 (openSUSE package)

Notes

Best solution so far is to manually delete those broken checksums to resume syncing.

The issue names the oc_filecache table and an upgrade from OC 10.5.0 to NC 21.0.0beta2; start by tracing where checksum values are migrated or validated during upgrade. Compare the proposed database cleanup with an occ command, then verify that a previously corrupted test-corrupt.txt can be edited and uploaded without a checksum mismatch.