[turbofan] Fix deopt loop in out-of-bounds string element access.

test/mjsunit/compiler/deopt-string-outofbounds.js

+// Copyright 2016 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.
+
+// Flags: --allow-natives-syntax
+
+var s = "12345";
+
+(function() {
+  function foo() { return s[5]; }
+
+  foo();
+  foo();
+  %OptimizeFunctionOnNextCall(foo);
+  foo();
+  %OptimizeFunctionOnNextCall(foo);
+  foo();
+  assertOptimized(foo);
+})();
+
+(function() {
+  function foo(i) { return s[i]; }
+
+  foo(0);
+  foo(1);
+  %OptimizeFunctionOnNextCall(foo);
+  foo(5);
+  %OptimizeFunctionOnNextCall(foo);
+  foo(5);
+  assertOptimized(foo);
+})();