Gracefully handle "doc_ids"=null in doc id replication filter option.
Gracefully handle "doc_ids"=null in doc id replication filter option.

Closes COUCHDB-1248

fkaempfer/couchdb,fkaempfer/couchdb,alanning/couchdb-couch,cloudant/couchdb-couch,alanning/couchdb-couch,smithsz/couchdb-couch,apache/couchdb-couch,apache/couchdb-couch,fkaempfer/couchdb,KlausTrainer/couchdb-couch,smithsz/couchdb-couch,ngpestelos/couchdb-couch,smithsz/couchdb-couch,apache/couchdb-couch,cloudant/couchdb-couch,alanning/couchdb-couch,ngpestelos/couchdb-couch,KlausTrainer/couchdb-couch,fkaempfer/couchdb,fkaempfer/couchdb,cloudant/couchdb-couch,fkaempfer/couchdb,KlausTrainer/couchdb-couch,ngpestelos/couchdb-couch