fix baichuan2 bug (#357)

Author: Jintao-Huang

swift/llm/utils/model.py

@@ -540,6 +540,11 @@ def get_model_tokenizer_baichuan2(model_dir: str,
                                   load_model: bool = True,
                                   model_config=None,
                                   **kwargs):
+    if model_config is None:
+        model_config = AutoConfig.from_pretrained(
+            model_dir, trust_remote_code=True)
+    if not hasattr(model_config, 'z_loss_weight'):
+        model_config.z_loss_weight = 0
     model, tokenizer = get_model_tokenizer_from_repo(
         model_dir,
         torch_dtype,