[sqlsmith] ERROR: plan should not reference subplan's variable

Updating master from f8c5855..1bdae16, sqlsmith triggers "failed to
generate plan" errors again.  Below is the smallest query logged so far.

regards,
Andreas

-- ERROR:  plan should not reference subplan's variable
set force_parallel_mode = 'on';
set max_parallel_workers_per_gather = '1';

explain WITH
jennifer_0 AS (select   (select b from public.rtest_v1 limit 1 offset 5)      as c0,
pg_catalog.pg_current_xlog_location()as c1,   sample_0.a as c2,   sample_0.a as c3 from   public.rtest_view4 as
sample_0tablesample system (5.9) where cast(null as bigint) = pg_catalog.hashinet(     cast((select client_addr from
pg_catalog.pg_stat_activitylimit 1 offset 35)        as inet)) limit 76)
 
select   ref_0.sl_name as c0 from   public.shoelace as ref_0 where (cast(null as anyrange) < cast(null as anyrange))
and(EXISTS (     select         39 as c0       from         jennifer_0 as ref_1       where cast(null as real) =
cast(nullas real)       limit 81)) limit 96;