When writing a tombstone, handle the case when doc body doesn't exist (#2557)
When writing a tombstone, handle the case when doc body doesn't exist (#2557)

Ensures xattr is updated correctly even when the doc body has already been deleted (import of an SDK delete scenario).
couchbaselabs/sync_gateway,couchbaselabs/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,tophatch/sync_gateway,tophatch/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,ceejatec/sync_gateway,ceejatec/sync_gateway