crypto/tls: fix broken looping code in windows root CA fetcher

R=alex.brainman, hectorchu, rsc
CC=golang-dev
https://golang.org/cl/5263045

root_windows.go

@@ -17,35 +17,31 @@ func loadStore(roots *x509.CertPool, name string) {
 		return
 	}
 
-	var prev *syscall.CertContext
+	var cert *syscall.CertContext
 	for {
-		cur := syscall.CertEnumCertificatesInStore(store, prev)
+		cert = syscall.CertEnumCertificatesInStore(store, cert)
-		if cur == nil {
+		if cert == nil {
 			break
 		}
 
-		var buf []byte
+		var asn1Slice []byte
-		hdrp := (*reflect.SliceHeader)(unsafe.Pointer(&buf))
+		hdrp := (*reflect.SliceHeader)(unsafe.Pointer(&asn1Slice))
-		hdrp.Data = cur.EncodedCert
+		hdrp.Data = cert.EncodedCert
-		hdrp.Len = int(cur.Length)
+		hdrp.Len = int(cert.Length)
-		hdrp.Cap = int(cur.Length)
+		hdrp.Cap = int(cert.Length)
 
-		cert, err := x509.ParseCertificate(buf)
+		buf := make([]byte, len(asn1Slice))
-		if err != nil {
+		copy(buf, asn1Slice)
-			continue
-		}
 
+		if cert, err := x509.ParseCertificate(buf); err == nil {
 			roots.AddCert(cert)
-		prev = cur
+		}
 	}
 
 	syscall.CertCloseStore(store, 0)
 }
 
 func initDefaultRoots() {
-	// TODO(brainman): To be fixed
-	return
-
 	roots := x509.NewCertPool()
 
 	// Roots