Add explicit null checks after string conversions in the shells.

include/v8.h

 // Copyright 2007-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 841 matching lines @@
   static Local<String> NewUndetectable(const uint16_t* data, int length = -1);
 
   /**
    * Converts an object to a utf8-encoded character array.  Useful if
    * you want to print the object.
    */
   class EXPORT Utf8Value {
    public:
     explicit Utf8Value(Handle<v8::Value> obj);
     ~Utf8Value();
-    char* operator*() { return str_; }
+    char* operator*() const { return str_; }
     int length() { return length_; }
    private:
     char* str_;
     int length_;
 
     // Disallow copying and assigning.
     Utf8Value(const Utf8Value&);
     void operator=(const Utf8Value&);
   };
 
   /**
    * Converts an object to an ascii string.
    * Useful if you want to print the object.
    */
   class EXPORT AsciiValue {
    public:
     explicit AsciiValue(Handle<v8::Value> obj);
     ~AsciiValue();
-    char* operator*() { return str_; }
+    char* operator*() const { return str_; }
     int length() { return length_; }
    private:
     char* str_;
     int length_;
 
     // Disallow copying and assigning.
     AsciiValue(const AsciiValue&);
     void operator=(const AsciiValue&);
   };
 
   /**
    * Converts an object to a two-byte string.
    */
   class EXPORT Value {
    public:
     explicit Value(Handle<v8::Value> obj);
     ~Value();
-    uint16_t* operator*() { return str_; }
+    uint16_t* operator*() const { return str_; }
     int length() { return length_; }
    private:
     uint16_t* str_;
     int length_;
 
     // Disallow copying and assigning.
     Value(const Value&);
     void operator=(const Value&);
   };
 };
@@ skipping 1553 matching lines @@
 
 }  // namespace v8
 
 
 #undef EXPORT
 #undef EXPORT_INLINE
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_