select for update can't work with global index

[Defined2014]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a int, b int, unique index(b), primary key(a)) partition by hash(a) partitions 5;
insert into t values (1,1),(2,2),(3,3),(4,4),(5,5);
begin;
select * from t use index(b) where b = 2 order by b limit 1 for update;

-- create another session
update t set b = 7 where b = 2;

2. What did you expect to see? (Required)

update blocked

3. What did you see instead (Required)

update success

4. What is your TiDB version? (Required)

[Defined2014]

Only affects IndexReader, it returns tblID instead of partitionID