Race condition in GROUP BY

There seems to be a concurrent read/write on a map when using the GROUP BY statement. This sample code reproduces the issue:

package ql_test

import (
        "database/sql"
        "fmt"
        "github.com/stretchr/testify/assert"
        "log"
        _ "modernc.org/ql/driver"
        "testing"
)

func TestGroupByRaceCondition(t *testing.T) {
        sess, err := sql.Open("ql2", "memory://database.ql")
        assert.NoError(t, err)

        tx, err := sess.Begin()
        _, err = tx.Exec(`CREATE TABLE artists (name string)`)
        assert.NoError(t, err)

        err = tx.Commit()
        assert.NoError(t, err)

        for i := 0; i < 100; i++ {
                tx, err := sess.Begin()
                assert.NoError(t, err)

                _, err = tx.Exec(`INSERT INTO artists (name) VALUES($1)`, fmt.Sprintf("artist-%d", i%5))
                assert.NoError(t, err)

                err = tx.Commit()
                assert.NoError(t, err)
        }

        rows, err := sess.Query(`SELECT name, count(1) from artists GROUP BY name`)
        assert.NoError(t, err)

        for rows.Next() {
                var name string
                var count int
                err := rows.Scan(&name, &count)
                assert.NoError(t, err)

                log.Printf("NAME: %v, COUNT: %v", name, count)
        }

}

The issue is visible when running the race condition detector:

go test -race -v -run TestGroupByRaceCondition *.go
=== RUN   TestGroupByRaceCondition
2020/12/20 18:38:45 NAME: artist-0, COUNT: 20
==================
WARNING: DATA RACE
Write at 0x00c00035fdc0 by goroutine 44:
  modernc.org/ql.(*selectFieldsGroupPlan).do.func1()
      /home/rev/go/src/modernc.org/ql/plan.go:2049 +0x10ad
  modernc.org/ql.(*groupByDefaultPlan).do()
      /home/rev/go/src/modernc.org/ql/plan.go:1684 +0xb6b
  modernc.org/ql.(*selectFieldsGroupPlan).do()
      /home/rev/go/src/modernc.org/ql/plan.go:2022 +0x1cc
  modernc.org/ql.(*DB).do()
      /home/rev/go/src/modernc.org/ql/ql.go:1479 +0x1fb
  modernc.org/ql.recordset.Do()
      /home/rev/go/src/modernc.org/ql/ql.go:75 +0x95
  modernc.org/ql.(*recordset).Do()
      <autogenerated>:1 +0xa4
  modernc.org/ql.newdriverRows.func1()
      /home/rev/go/src/modernc.org/ql/driver.go:449 +0x101