Add missing guard to 'AsPythonObjectNode.doNativeObject'.

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/CExtNodes.java

@@ -160,7 +160,7 @@ PythonAbstractObject doNativeWrapper(PythonObjectNativeWrapper object) {
             return object.getPythonObject();
         }
 
-        @Specialization(guards = "isForeignObject(object)")
+        @Specialization(guards = {"isForeignObject(object)", "!isNativeWrapper(object)"})
         PythonAbstractObject doNativeObject(TruffleObject object) {
             return factory().createNativeObjectWrapper(object);
         }
@@ -204,6 +204,10 @@ protected boolean isForeignObject(TruffleObject obj) {
             return getClassNode.execute(obj) == getCore().getForeignClass();
         }
 
+        protected boolean isNativeWrapper(Object obj) {
+            return obj instanceof PythonNativeWrapper;
+        }
+
         @TruffleBoundary
         public static Object doSlowPath(Object object) {
             if (object instanceof PythonObjectNativeWrapper) {