fix TransfoXLModel loading

pytorch_pretrained_bert/modeling_transfo_xl.py

@@ -959,7 +959,12 @@ class TransfoXLPreTrainedModel(nn.Module):
             for name, child in module._modules.items():
                 if child is not None:
                     load(child, prefix + name + '.')
-        load(model, prefix='')
+
+        start_prefix = ''
+        if not hasattr(model, 'transformer') and any(s.startswith('transformer.') for s in state_dict.keys()):
+            start_prefix = 'transformer.'
+        load(model, prefix=start_prefix)
+
         if len(missing_keys) > 0:
             logger.info("Weights of {} not initialized from pretrained model: {}".format(
                 model.__class__.__name__, missing_keys))