improve: add explicit error handling for empty API responses

Co-Authored-By: Junyan Qin <Chin> <rockchinq@gmail.com>

pkg/provider/runners/difysvapi.py

@@ -146,6 +146,9 @@ class DifyServiceAPIRunner(runner.RequestRunner):
                         content=self._try_convert_thinking(basic_mode_pending_chunk),
                     )
                     basic_mode_pending_chunk = ''
+        
+        if chunk is None:
+            raise errors.DifyAPIError("Dify API 没有返回任何响应，请检查网络连接和API配置")
 
         query.session.using_conversation.uuid = chunk["conversation_id"]
 
@@ -238,6 +241,9 @@ class DifyServiceAPIRunner(runner.RequestRunner):
                         )
                 if chunk['event'] == 'error':
                     raise errors.DifyAPIError("dify 服务错误: " + chunk['message'])
+        
+        if chunk is None:
+            raise errors.DifyAPIError("Dify API 没有返回任何响应，请检查网络连接和API配置")
 
         query.session.using_conversation.uuid = chunk["conversation_id"]