Fixed projection push down bug.

Please see the following example query. The following query will cause missing projected expression bugs.

select
  n1.n_nationkey,
  n1.n_name,
  n2.n_name
from nation n1 join (select * from nation union select * from nation) n2 on substr(n1.n_name, 1, 4) = substr(n2.n_name, 1, 4)
order by n1.n_nationkey;