traceback object init - set it to empty only if null

py/objexcept.c

@@ -558,10 +558,9 @@ void mp_obj_exception_add_traceback(mp_obj_t self_in, qstr file, size_t line, qs
         if (self->traceback == NULL) {
             self->traceback = &MP_STATE_VM(mp_emergency_traceback_obj);
         }
-    }
-
         // populate traceback object
         *self->traceback = mp_const_empty_traceback_obj;
+    }
 
     // append the provided traceback info to traceback data
     // if memory allocation fails (eg because gc is locked), just return