debug/pe: use bytes.IndexByte instead of a loop

Follow CL 98759

Change-Id: I58c8b769741b395e5bf4e723505b149d063d492a
Reviewed-on: https://go-review.googlesource.com/99095
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/debug/pe/string.go

@@ -5,6 +5,7 @@
 package pe
 
 import (
+	"bytes"
 	"encoding/binary"
 	"fmt"
 	"io"
@@ -13,8 +14,9 @@ import (
 // cstring converts ASCII byte sequence b to string.
 // It stops once it finds 0 or reaches end of b.
 func cstring(b []byte) string {
-	var i int
-	for i = 0; i < len(b) && b[i] != 0; i++ {
+	i := bytes.IndexByte(b, 0)
+	if i == -1 {
+		i = len(b)
 	}
 	return string(b[:i])
 }