There is a bug (or maybe just a questionable behavior) where PostReview
doesn't update the postSubmit bit on a 0 vote in ReviewDb even if the
vote was made after submission. This was causing a difference from
NoteDb in this test, since NoteDb was recording this 0 vote as
postSubmit.
Rather than delve too deeply into PostReview at this time, just fix the
test to handle the more common case of a nonzero label. Note that the
new test assertion would have failed under ReviewDb (but not NoteDb)
if we left the vote value at 0.
Change-Id: I1c71ace23693a0c27bb60a0d6e8202a719e0477a
894b74566c