the rows.NextResultSet() will always be blocked, if the second query result is error.

[yireyun]

Issue description

When the query returns multiple result sets, if the second query result is wrong, it will not return when calling rows.nextresultset (), and the call will always be blocked.

Example code

// queryMulti
package main

import (
	"database/sql"
	"fmt"

	_ "github.com/go-sql-driver/mysql"
)

func queryMulti() (err error) {
	sqlText := "" +
		"select 'ds1' ds, ifnull(null,'') sex1  ;" +
		"select 'ds2' ds, isnull(null,'') sex2  ;"
	connectionString := "root:game@tcp(192.168.1.88:3306)/GMDB?charset=utf8&multiStatements=true"
	my, err := sql.Open("mysql", connectionString)
	if err != nil {
		fmt.Printf("Open %v\n", err)
		return err
	} else {
		fmt.Printf("Open Success: %v,\n\tStats%v\n", connectionString, my.Stats())
	}

	defer my.Close()

	rows, err := my.Query(sqlText)
	if err != nil {
		fmt.Printf("Query : %v\n", err)
		return err
	}
	defer rows.Close()

	var id, sex string
	var ds, dsr = 1, 1
	for rows.Next() {
		if err := rows.Scan(&id, &sex); err != nil {
			fmt.Printf("Scan Error: %v\n", err)
			return err
		} else {
			fmt.Printf("DS[%2v]Row[%2v] => id[%v], sex[%v]\n",
				ds, dsr, id, sex)
			dsr++
		}
	}
	for rows.NextResultSet() { // <-- blocked
		ds++
		for rows.Next() {
			if err := rows.Scan(&id, &sex); err != nil {
				fmt.Printf("Scan %v\n", err)
				return err
			} else {
				fmt.Printf("DS[%2v]Row[%2v] => id[%v], sex[%v]\n",
					ds, dsr, id, sex)
				dsr++
			}
		}
	}
	return nil
}

func main() {

	if err := queryMulti(); err != nil {
		fmt.Printf("queryMulti : %v\n", err)
	}
}

Error log

Configuration

*Driver version (or git SHA):Release v1.5.0 (#1047) git: 17ef3dd

*Go version:1.12.15

*Server version:MySQL 5.22

*Server OS: ubuntu

fix fork:
yireyun@eac50bb

[ChaimHong]

@methane @julienschmidt @arnehormann @jszwec
yireyun@eac50bb
Review please

[methane]

Fixed in #1462