Fix setting empty path to subdoc mutation
Fix setting empty path to subdoc mutation

Change-Id: Id051998e1b3077f1ac076c6ce23672e81fbb33d2
Reviewed-on: http://review.couchbase.org/119308
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Ellis Breen <9d8041ac7ead8d3e1f3217c04c7ed5e3098c2381@couchbase.com>

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