Fix Smi::IsValid assert in StringCharCodeAt deferred code.

test/mjsunit/string-charcodeat.js

Index: test/mjsunit/string-charcodeat.js
diff --git a/test/mjsunit/string-charcodeat.js b/test/mjsunit/string-charcodeat.js
index 831f688fd4538c6cbd8b13b8c29bffc6a4759e4e..fb7ab9af86c3505df9aac480e8757a7bca5789e3 100644
--- a/test/mjsunit/string-charcodeat.js
+++ b/test/mjsunit/string-charcodeat.js
@@ -153,6 +153,17 @@ TestStringType(Slice16End, true);
 TestStringType(Flat16, true);
 TestStringType(NotAString16, true);
 
+
+function ConsNotSmiIndex() {
+  var str = Cons();
+  assertTrue(isNaN(str.charCodeAt(0x7fffffff)));
+}
+
+for (var i = 0; i < 100000; i++) {
+  ConsNotSmiIndex();
+}
+
+
 for (var i = 0; i != 10; i++) {
   assertEquals(101, Cons16().charCodeAt(1.1));
   assertEquals('e', Cons16().charAt(1.1));