Regression in bulk insert behavior

The following query _should_ be able to be executed in bulk:

```sql
INSERT INTO users (id, name) VALUES (1, 'foo'), (2, 'bar') /* insert multiple users in one query */
```

With mysqlclient 1.3.6, this query is emitted as a bulk insert.

I upgraded mysqclient to 1.3.9, and suddenly, this query is emitted as two individual inserts.