MB-9907: Assume correct length of valueBlob

- Additional refactoring

Change-Id: I9415fada610e9f4ed18e7ad606ff5c42cd44ec49
Reviewed-on: http://review.couchbase.org/32363
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Volker Mische <volker.mische@gmail.com>