CBL-1194: update the log (#2720)
CBL-1194: update the log (#2720)

* check for error, if error show a warning.
* check cookie exists, if not print a verbose log and return empty
couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios