fix: simplify condition checks for mcp_servers in base_chat_step.py and base_chat_node.py

Author: liuruibin

apps/application/chat_pipeline/step/chat_step/impl/base_chat_step.py

@@ -234,7 +234,7 @@ def _handle_mcp_request(self, mcp_source, mcp_servers, mcp_tool_ids, tool_ids,
         # 兼容老数据
         if not mcp_tool_ids:
             mcp_tool_ids = []
-        if mcp_source == 'custom' and mcp_servers is not None and '"stdio"' not in mcp_servers:
+        if mcp_source == 'custom' and mcp_servers and '"stdio"' not in mcp_servers:
             mcp_servers_config = json.loads(mcp_servers)
         elif mcp_tool_ids:
             mcp_tools = QuerySet(Tool).filter(id__in=mcp_tool_ids).values()

apps/application/flow/step_node/ai_chat_step_node/impl/base_chat_node.py

@@ -221,7 +221,7 @@ def _handle_mcp_request(self, mcp_source, mcp_servers, mcp_tool_id, mcp_tool_ids
             mcp_tool_ids = []
         if mcp_tool_id:
             mcp_tool_ids = list(set(mcp_tool_ids + [mcp_tool_id]))
-        if mcp_source == 'custom' and mcp_servers is not None and '"stdio"' not in mcp_servers:
+        if mcp_source == 'custom' and mcp_servers and '"stdio"' not in mcp_servers:
             mcp_servers_config = json.loads(mcp_servers)
             mcp_servers_config = self.handle_variables(mcp_servers_config)
         elif mcp_tool_ids: