Blob files are all deleted after running repair

[jonas0616]

When running the repair on a RocksDB database with BlobDB enabled, the repair process completes sucessfully.
However, after the repair, all references to the blob files are missing from the MANIFEST file.
As a result, when the database is opened again, all the blob files are automatically deleted.
This issue is quite alarming; the intention was to repair RocksDB, but instead, it ended up wiping all the data.

Expected behavior

Before running repair, the MANIFEST file includes the blob files' information:

$ ldb manifest_dump --path=MANIFEST-000038 --hex | grep -A 3 'blob files'
--- blob files --- version# 2 ---
blob_file_number: 14 total_blob_count: 1 total_blob_bytes: 380 checksum_method:  checksum_value:  linked_ssts: { 13 } garbage_blob_count: 0 garbage_blob_bytes: 0
blob_file_number: 18 total_blob_count: 1 total_blob_bytes: 380 checksum_method:  checksum_value:  linked_ssts: { 33 } garbage_blob_count: 0 garbage_blob_bytes: 0
blob_file_number: 22 total_blob_count: 1 total_blob_bytes: 380 checksum_method:  checksum_value:  linked_ssts: { 21 } garbage_blob_count: 0 garbage_blob_bytes: 0

Actual behavior

After running repair, the blob files are no longer present in the MANIFEST file:

$ ldb manifest_dump --path=MANIFEST-000003 --hex | grep -A 3 'blob files'

Steps to reproduce the behavior

1. Create a RocksDB database with BlobDB enabled.
2. Insert data that generates blob files.
3. Manually flush the database.
4. Run repair on the database.
5. Use ldb to check the MANIFEST after the repair - blob files are missing.
6. Reopen the database, and observe that all blob files are deleted.