Fix broken unit test "test rollback to zero on consumer"

This fixes a segfault on ubuntu and centos.

Change-Id: Ie0d889e1d85764e31155e868ac2698ebd38559cc
Reviewed-on: http://review.couchbase.org/37001
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>