cannot restore the metakv when there are only write cf files

[Leavrth]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. start log backup
   2.create table test.t(id int);
2. insert into test.t values (1)
3. do snapshot backup
4. insert into test.t with 30000 rows
5. restore to another cluster

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

the next_rowid shoule be 60001, and there are 30002 rows in the table test.t.

3. What did you see instead (Required)

the next_rowid is 30001, and there are 30002 rows in the table test.t.

4. What is your TiDB version? (Required)

master