Some delete mutations with xattrs not being indexed

Sync Gateway recently completed uptake of a kv-engine enhancement to support delete of document body and xattr update in a single multi-part subdoc operation. Previously we were limited to a two-operation process - deleting the document in the first op, then updating the xattr in a second op.

After uptaking this change, delete mutations that delete the body and update the xattr don't appear to be indexed by the view-engine - view results omit those doc ids.

Two-part deletes are still appearing in the view, so I'm confident that we're properly setting the flag to index xattrs/tombstones on the design doc.

I compared the DCP mutations for the two cases to try to identify the difference in the delete mutations for the two cases. The main difference I see is in the Data Type. The single operation results in a DCP delete mutation with Data Type 0x05 (JSON + XATTR), while the two-part operations results in a DCP delete mutation with Data Type 0x04 (XATTR).

I'll attached packet captures for the two DCP mutations in case that's useful.