Fix the case of no words to copy.

src/utils.h

 // Copyright 2006-2008 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 582 matching lines @@
   }
 #endif
 
 #undef STOS
 }
 
 
 // Copies data from |src| to |dst|.  The data spans MUST not overlap.
 inline void CopyWords(Object** dst, Object** src, int num_words) {
   ASSERT(Min(dst, src) + num_words <= Max(dst, src));
+  ASSERT(num_words > 0);
+
   // Use block copying memcpy if the segment we're copying is
   // enough to justify the extra call/setup overhead.
   static const int kBlockCopyLimit = 16;
 
   if (num_words >= kBlockCopyLimit) {
     memcpy(dst, src, num_words * kPointerSize);
   } else {
     int remaining = num_words;
     do {
       remaining--;
@@ skipping 39 matching lines @@
 
   Dest dest;
   memcpy(&dest, &source, sizeof(dest));
   return dest;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_UTILS_H_