Fix Bulk counter for negative Delta
Fix Bulk counter for negative Delta

Change-Id: I36e2f21d8c2195b32dcb164bd9e4cd2ba0b1cb1c
Reviewed-on: http://review.couchbase.org/70246
Reviewed-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

brett19/gocb