CCBC-1514: do not translate unknown error with "item-only" attribute
CCBC-1514: do not translate unknown error with "item-only" attribute

The library should not translate unknown errors with "item-only"
attributes into LCB_ERR_CAS_MISMATCH

Change-Id: I9ae07cfb0a7dd530d25449511a2fddaaed4db47b
Reviewed-on: https://review.couchbase.org/c/libcouchbase/+/165369
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: David Kelly <d83cd2a93a916ce0b0d4c1349b44be044799feca@gmail.com>

couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase