create same name table should not successful before drop table is not finished.

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

1. create a table with 1T size
2. execute admin check index to check data consistency
3. before "admin check index" finished, execute "drop table items"
4. ddl will blocked, then use "show tables" check that the old table has been non-existed
5. create table with same name

### 2. What did you expect to see? (Required)
same name table should not be created before drop table ddl finished
### 3. What did you see instead (Required)
create table successfully.
### 4. What is your TiDB version? (Required)

master