Fix data race with Rows and ConnPool

In an effort to reduce memory allocations, Rows was stored on the
Conn. This caused a race condition where Rows are closed and this
returns the Conn to the Pool. The Pool could then give out the Conn
again. Rows would then be reanimated and the original Rows could reclose
it.

conn.go

@@ -53,7 +53,6 @@ type Conn struct {
 	alive              bool
 	causeOfDeath       error
 	logger             Logger
-	rows               Rows
 	mr                 msgReader
 }
 

conn_pool_test.go

@@ -410,6 +410,50 @@ func TestConnPoolQuery(t *testing.T) {
 	}
 }
 
+func TestConnPoolQueryConcurrentLoad(t *testing.T) {
+	t.Parallel()
+
+	pool := createConnPool(t, 10)
+	defer pool.Close()
+
+	for i := 0; i < 100; i++ {
+		go func(i int) {
+			var rowCount int32
+
+			rows, err := pool.Query("select generate_series(1,$1)", 1000)
+			if err != nil {
+				fmt.Println(i, err)
+				t.Fatalf("pool.Query failed: %v", err)
+			}
+			defer rows.Close()
+
+			for rows.Next() {
+				var n int32
+				err = rows.Scan(&n)
+				if err != nil {
+					fmt.Println(i, err)
+					t.Fatalf("rows.Scan failed: %v", err)
+				}
+				if n != rowCount+1 {
+					fmt.Println(i, err)
+					t.Fatalf("Expected n to be %d, but it was %d", rowCount+1, n)
+				}
+				rowCount++
+			}
+
+			if rows.Err() != nil {
+				fmt.Println(i, err)
+				t.Fatalf("conn.Query failed: ", err)
+			}
+
+			if rowCount != 1000 {
+				fmt.Println(i, err)
+				t.Error("Select called onDataRow wrong number of times")
+			}
+		}(i)
+	}
+}
+
 func TestConnPoolQueryRow(t *testing.T) {
 	t.Parallel()
 

query.go

@@ -354,8 +354,7 @@ func (rows *Rows) Values() ([]interface{}, error) {
 // be returned in an error state. So it is allowed to ignore the error returned
 // from Query and handle it in *Rows.
 func (c *Conn) Query(sql string, args ...interface{}) (*Rows, error) {
-	c.rows = Rows{conn: c, startTime: time.Now(), sql: sql, args: args, logger: c.logger}
+	rows := &Rows{conn: c, startTime: time.Now(), sql: sql, args: args, logger: c.logger}
-	rows := &c.rows
 
 	ps, ok := c.preparedStatements[sql]
 	if !ok {