BUG: table.sort_by().count() generates incorrect code

[cpcloud]

In [1]: con = ibis.postgres.connect(database='ibis_testing')

In [2]: t = con.table('batting')

In [3]: print(t.sort_by(ibis.desc(t.playerID)).count().compile().compile())
SELECT count(%(count_1)s) AS count 
FROM batting AS t0 ORDER BY t0."playerID" DESC

This is incorrect, because ORDER BY in an aggregation is meaningless without a GROUP BY.