Slow log shows success for the query that doesn't send all the rows

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```java
stmt.setFetchSize(Integer.MIN_VALUE);

rs = stmt.executeQuery("SELECT * FROM t_order ORDER BY name DESC");
String sql="";
while(rs.next()) {
sql = rs.getString(1);
System.out.println("sql="+sql);
Thread.sleep(200);
}
...
```

After some time, terminate the client.

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

Slow log shows `succeed: false`.

### 3. What did you see instead (Required)

TiDB log shows `command dispatch failed, err="connection was bad"`, while slow log shows `succeed: true`.

### 4. What is your TiDB version? (Required)

master