Iad564dd47 was problematic in the error case because it returned
Predicate.not(Predicate.any()). The "any" predicate is not an index
predicate, which produces at least two problems:
* When used in a with another non-index predicate, it
might throw "no ChangeDataSource" from AndSource/OrSource.
* More dangerously, when combined with an index predicate, it is used as
a post-filtering predicate. A post-filtering predicate that matches no
results means it gets applied to every change in the index before
returning an empty set, which is bad.
Instead, reuse a handy existing index predicate that is designed to
return no results efficiently from the index:
ChangeStatusPredicate.NONE. Expose this from a more general location,
ChangeIndexPredicate#none().
Change-Id: Ic9a7e277070cff7768ec91c1972cf8e9f6deacb1
d9679cdb60