Assert failure in TPC-H Q8

with `lineitem` and `orders` distributed and all other tables reference tables:

```
TRAP: FailedAssertion("!(currentAnchorTable != ((void *)0))", File: "planner/multi_join_order.c", Line: 1004) [151/1870]
2018-12-13 04:48:29.313 CET [69596] LOG: server process (PID 69652) was terminated by signal 6: Aborted
2018-12-13 04:48:29.313 CET [69596] DETAIL: Failed process was running: select
o_year,
sum(case
when nation = 'BRAZIL' then volume
else 0
end) / sum(volume) as mkt_share
from
(
select
extract(year from o_orderdate) as o_year,
l_extendedprice * (1 - l_discount) as volume,
n2.n_name as nation
from
part,
supplier,
lineitem,
orders,
customer,
nation n1,
nation n2,
region
where
p_partkey = l_partkey
and s_suppkey = l_suppkey
and l_orderkey = o_orderkey
and o_custkey = c_custkey
and c_nationkey = n1.n_nationkey
and n1.n_regionkey = r_regionkey
and r_name = 'AMERICA'
and s_nationkey = n2.n_nationkey
and o_orderdate between date '1995-01-01' and date '1996-12-31'
and p_type = 'ECONOMY ANODIZED STEEL'
) as all_nations
group by
o_year
order by
o_year;
```