add index on dxf, incorrect row count if failed to update it on done

[D3Hunter]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

reorg ctx is removed on done, but if the txn failed, we will retry

tidb/pkg/ddl/reorg.go

Line 414 in 3c40731

d.removeReorgCtx(job.ID)

but at that time we didn't set rowcount

tidb/pkg/ddl/index.go

Lines 2512 to 2517 in 3c40731

	if task.State == proto.TaskStateSucceed {
	logutil.DDLLogger().Info(
	"task succeed, start to resume the ddl job",
	zap.String("task-key", taskKey))
	return nil
	}

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

master