data inconsistency during adding unique index

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

``` SQL
func TestInsertIgnore2(t *testing.T) {
store, dom := testkit.CreateMockStoreAndDomain(t)
defer ingesttestutil.InjectMockBackendMgr(t, store)()

tk := testkit.NewTestKit(t, store)
tk.MustExec("use test")
tk.MustExec("create table t(a int DEFAULT '-13202', b varchar(221) NOT NULL DEFAULT 'duplicatevalue', " +
"c int NOT NULL DEFAULT '0', PRIMARY KEY (c, b));")

tk1 := testkit.NewTestKit(t, store)
tk1.MustExec("use test")

d := dom.DDL()
originalCallback := d.GetHook()
defer d.SetHook(originalCallback)
callback := &callback.TestDDLCallback{}

tk1.Exec("INSERT INTO t VALUES (-18585,'duplicatevalue',0);")

onJobUpdatedExportedFunc := func(job *model.Job) {
switch job.SchemaState {
case model.StateDeleteOnly:
_, err := tk1.Exec("REPLACE INTO t VALUES (-18585,'duplicatevalue',1);")
assert.NoError(t, err)
}
}
callback.OnJobUpdatedExported.Store(&onJobUpdatedExportedFunc)
d.SetHook(callback)

tk3 := testkit.NewTestKit(t, store)
tk3.MustExec("use test")
ddl.MockDMLExecutionStateBeforeImport = func() {
tk3.MustExec("insert ignore INTO t VALUES (-18585,'duplicatevalue',1), (-18585,'duplicatevalue',3);")
}

require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/pkg/ddl/mockDMLExecutionStateBeforeImport", "return(true)"))
tk.MustExec("alter table t add unique index idx(b);")
tk.MustExec("admin check table t;")
require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/pkg/ddl/mockDMLExecutionStateBeforeImport"))
}
```

### 2. What did you expect to see? (Required)
Test passes.
### 3. What did you see instead (Required)
```
[admin:8223]data inconsistency in table: t, index: idx, handle: {0, duplicatevalue}, index-values:"" != record-values:"handle: {0, duplicatevalue}, values: [KindString duplicatevalue]"
```
### 4. What is your TiDB version? (Required)
nightly