Fix 'illegal access' in Date constructor edge case

test/mjsunit/regress/regress-4640.js

Index: test/mjsunit/regress/regress-4640.js
diff --git a/test/mjsunit/regress/regress-4640.js b/test/mjsunit/regress/regress-4640.js
new file mode 100644
index 0000000000000000000000000000000000000000..ed609bbb1f14816d05306a7a84dc577a111a2593
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+++ b/test/mjsunit/regress/regress-4640.js
@@ -0,0 +1,19 @@
+// Copyright 2015 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.
+
+// Some surrounding cases which already worked, for good measure
+assertTrue(new Date('275760-10-14') == 'Invalid Date');
+assertTrue(new Date('275760-09-23') == 'Invalid Date');
+assertTrue(new Date('+275760-09-24') == 'Invalid Date');
+assertTrue(new Date('+275760-10-13') == 'Invalid Date');
+
+// The following cases used to throw "illegal access"
+assertTrue(new Date('275760-09-24') == 'Invalid Date');
+assertTrue(new Date('275760-10-13') == 'Invalid Date');
+assertTrue(new Date('+275760-10-13 ') == 'Invalid Date');
+
+// However, dates within the range or valid
+assertTrue(new Date('100000-10-13') != 'Invalid Date');
+assertTrue(new Date('+100000-10-13') != 'Invalid Date');
+assertTrue(new Date('+100000-10-13 ') != 'Invalid Date');