fix(bigquery): RowIterator.Schema not filled when using Storage Read API

[alvarowolfx]

Found an issue when reading a query and unmarshalling to a user defined struct. See code sample:

type UserStruct struct {
    Name string
    Number  int
    State string
}

// Enable Storage API usage for fetching data
err = client.EnableStorageReadClient(ctx)
if err != nil {
    // TODO: Handle error.
}

sql := fmt.Sprintf(`SELECT name, number, state FROM %s WHERE state = "CA"`, `bigquery-public-data.usa_names.usa_1910_current`)

q := client.Query(sql)
it, err := q.Read(ctx)
if err != nil {
    // TODO: Handle error.
}
for {
    var s UserStruct
    err := it.Next(&s)
    if err == iterator.Done {
        break
    }
    if err != nil {
        // TODO: Handle error.
    }
    fmt.Println(s)
}
// Output 
// { 0 }
// { 0 }
// { 0 }

The target struct was returning with it's zero value, not being filled with data.

[shollyman]

Generally seems fine, one question around the test query driving the test.

[shollyman]

ship it!