MB-9549 Fix to the memory leak in GetAndUpdateTTL

This is a regression from 2.2.0, which causes a memory leak
when we update the TTL for a non-resident item.

Change-Id: I3dfd9dcd09a0acfdcd2cd6623f75ca54916d1116
Reviewed-on: http://review.couchbase.org/30303
Reviewed-by: Sundararaman Sridharan <sundar.sridharan@gmail.com>
Tested-by: Sundararaman Sridharan <sundar.sridharan@gmail.com>