Fix one more missing c0_ < 0 check in scanner

BUG=chromium:433766
LOG=n
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/731953003

Cr-Commit-Position: refs/heads/master@{#25371}

src/scanner.cc

@@ -312,8 +312,7 @@ Token::Value Scanner::SkipSourceURLComment() {
 void Scanner::TryToParseSourceURLComment() {
   // Magic comments are of the form: //[#@]\s<name>=\s*<value>\s*.* and this
   // function will just return if it cannot parse a magic comment.
-  if (!unicode_cache_->IsWhiteSpace(c0_))
-    return;
+  if (c0_ < 0 || !unicode_cache_->IsWhiteSpace(c0_)) return;
   Advance();
   LiteralBuffer name;
   while (c0_ >= 0 && !unicode_cache_->IsWhiteSpaceOrLineTerminator(c0_) &&

test/mjsunit/regress/regress-crbug-433766.js

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var filler = "//" + new Array(('@')).join('x');
+
+// Test strict eval in global context.
+eval(
+  "'use strict';" +
+  "var x = 23;" +
+  "var f = function bozo1() {" +
+  "  return x;" +
+  "};" +
+  "f;" +
+  filler
+)();