Tiny fix to grokdump heap stats printer

tools/grokdump.py

 #!/usr/bin/env python
 #
 # Copyright 2012 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
@@ skipping 3124 matching lines @@
           if maybe_address_contents == 0xdecade00:
             in_oom_dump_area = True
         heap_object = heap.FindObject(maybe_address)
         maybe_symbol = reader.FindSymbol(maybe_address)
         oom_comment = ""
         if in_oom_dump_area:
           if maybe_address_contents == 0xdecade00:
             oom_comment = " <----- HeapStats start marker"
           elif maybe_address_contents == 0xdecade01:
             oom_comment = " <----- HeapStats end marker"
-          else:
+          elif maybe_address_contents is not None:
             oom_comment = " %d (%d Mbytes)" % (maybe_address_contents,
                                             maybe_address_contents >> 20)
         if slot == frame_pointer:
           maybe_symbol = "<---- frame pointer"
           frame_pointer = maybe_address
         print "%s: %s %s %s%s" % (reader.FormatIntPtr(slot),
                                   reader.FormatIntPtr(maybe_address),
                                    "".join(ascii_content),
                                    maybe_symbol or "",
                                    oom_comment)
@@ skipping 34 matching lines @@
     try:
       server = InspectionWebServer(PORT_NUMBER, options, args[0])
       print 'Started httpserver on port ' , PORT_NUMBER
       webbrowser.open('http://localhost:%i/summary.html' % PORT_NUMBER)
       server.serve_forever()
     except KeyboardInterrupt:
       print '^C received, shutting down the web server'
       server.socket.close()
   else:
     AnalyzeMinidump(options, args[0])