Submitted by: @dyemanov

recreate table t (id int not null);
alter table t add constraint pk primary key (id);

insert into t values (1);
commit;

select *
from t t1, t t2, t t3, t t4
where http://t1.id = http://t2.id
and http://t2.id = http://t3.id
and http://t3.id = http://t4.id
PLAN MERGE (JOIN (T1 NATURAL, T2 INDEX (PK)), JOIN(T3 NATURAL, T4 INDEX (PK)))

the engine reports:
PLAN JOIN (MERGE (SORT (JOIN (T3 NATURAL, T4 INDEX (PK))), SORT (JOIN (T1 NATURAL, T2 INDEX (PK)))), JOIN ())

and crashes in rse.cpp because of rsb_count == 0 (in the last join).

Commits: 6729422 eecccbb