MB-10274 Fix partial update message pattern matching

This message is now a tuple with arity 4, not 3 anymore.

Change-Id: I81c4677d96061ad3221ca7f4a543c1e0cdbe1158
Reviewed-on: http://review.couchbase.org/33828
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>