Failed assertion in joininfo.c, remove_join_clause_from_rels

Hi,

SQLsmith found a failing Assertion in joininfo.c on master.  I can
reproduce it on an assertion-enabled build like this:

create table t1(a int primary key);
create table t2(a int);

select * from t2 right join
         (t1 as t1a inner join t1 as t1b on t1a.a = t1b.a)
      on t1a.a is not null and exists (select);

-- TRAP: failed Assert("list_member_ptr(rel->joininfo, restrictinfo)"), File: "joininfo.c", Line: 144, PID: 777839

regards,
Andreas