Fix null dereference after OOM.

src/debug.cc

 // 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
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 768 matching lines @@
 
   // Check for caught exceptions.
   if (caught_exception) {
     ASSERT(!isolate->has_pending_exception());
     MessageLocation computed_location;
     isolate->ComputeLocation(&computed_location);
     Handle<Object> message = MessageHandler::MakeMessageObject(
         "error_loading_debugger", &computed_location,
         Vector<Handle<Object> >::empty(), Handle<String>(), Handle<JSArray>());
     ASSERT(!isolate->has_pending_exception());
-    isolate->set_pending_exception(*exception);
-    MessageHandler::ReportMessage(Isolate::Current(), NULL, message);
-    isolate->clear_pending_exception();
+    if (!exception.is_null()) {
+      isolate->set_pending_exception(*exception);
+      MessageHandler::ReportMessage(Isolate::Current(), NULL, message);
+      isolate->clear_pending_exception();
+    }
     return false;
   }
 
   // Mark this script as native and return successfully.
   Handle<Script> script(Script::cast(function->shared()->script()));
   script->set_type(Smi::FromInt(Script::TYPE_NATIVE));
   return true;
 }
 
 
@@ skipping 2969 matching lines @@
     {
       Locker locker;
       Isolate::Current()->debugger()->CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal