## Context
Error is caused due to these steps:
- File is uploaded to Home server and attempts to import
- Import ends up in `claimDocument` in `HostedStorageManager`
- Tries to read doc metadata from DocWorkerMap, gets 'unknown' as md5 hash
- Thinks local doc is out of date and erases it.
- Downloads a non-existent file from S3, so import fails as it has no data.
## Proposed solution
This fixes it by checking for DummyDocWorker's special 'unknown' MD5, forcing an S3 check.
## Related issues
https://community.getgrist.com/t/no-metadata-for-imported-grist-document/6029/32