CBG-4989 don't panic if no _vv but _sync.rev.ver on import

[torcolvin]

CBG-4989 don't panic if no _vv but _sync.rev.ver on import

I don't think this critical because I'm not sure how you'd end up in this scenario outside of tests where you have _sync.vv.ver but not _vv. This will backport into 4.0.2 but isn't urgent.

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

[Copilot]

Pull Request Overview

This PR addresses a panic condition when importing documents that have _sync.rev.ver but lack the _vv xattr, a scenario that can occur in test environments.

Key Changes:

• Modified type declaration from interface to concrete pointer type to prevent nil pointer dereference
• Added test case to verify the fix handles the edge case without panicking

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
db/import_listener.go	Changed cv variable type from cvExtractor interface to *rawHLV pointer to safely handle nil case
db/import_test.go	Added test that removes _vv xattr after document creation to reproduce and verify the panic scenario