net: fix windows build

R=rsc, bradfitz
CC=golang-dev
https://golang.org/cl/5661055

src/pkg/net/fd_windows.go

@@ -5,6 +5,7 @@
 package net
 
 import (
+	"errors"
 	"io"
 	"os"
 	"runtime"
@@ -518,7 +519,7 @@ func (o *acceptOp) Name() string {
 
 func (fd *netFD) accept(toAddr func(syscall.Sockaddr) Addr) (*netFD, error) {
 	if err := fd.incref(false); err != nil {
-		return 0, err
+		return nil, err
 	}
 	defer fd.decref()
 

src/pkg/net/sendfile_windows.go

@@ -50,7 +50,7 @@ func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
 
 	c.wio.Lock()
 	defer c.wio.Unlock()
-	if err := c.incref(); err != nil {
+	if err := c.incref(false); err != nil {
 		return 0, err, true
 	}
 	defer c.decref()