SELECT fails with a disjunct and small LIMIT

[Kostja Osipov]

When SELECT limit is small (below 7), SELECT fails with ERR_CODE_ILLEGAL_PARAMETERS
Select(key1, key2, { use_index => 1, limit=$N })

Test suite test case (box_big configuration, namespace 0):

exec sql "insert into t0 values ('Doe', 'Richard')"
exec sql "insert into t0 values ('Roe', 'Richard')"
exec sql "insert into t0 values ('Woe', 'Richard')"
exec sql "insert into t0 values ('Major', 'Tomas')"
exec sql "insert into t0 values ('Kytes', 'Tomas')"
exec sql "insert into t0 values ('Stiles', 'Tomas')"
exec sql "insert into t0 values ('Wales', 'Tomas')"
exec sql "insert into t0 values ('Callaghan', 'Tomas')"
# xxx: bug
exec sql "select * from t0 where k1='Richard' or k1='Tomas' or k1='Tomas' limit 5"