Fix loss-of-context bug with endure.

Fixed bug which causes endure to fail hard when a couchbase error occurs.

Change-Id: I5eb590f06d35670a42e7f524e91575aa0d6caa9d
Reviewed-on: http://review.couchbase.org/23844
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>