Fix reply filter for open_revs
Fix reply filter for open_revs

In general, in an absence of latest attribute, we expect
one reply per passed in revision which could be either
doc or not found.

This fix's making sure that we are removing not_found's
only for the revisions that also have {ok, Doc} reply.

COUCHDB-3097

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb