fix: handle case where tool is None in tool activation check

Author: liuruibin

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

@@ -257,7 +257,7 @@ def _handle_mcp_request(self, mcp_enable, tool_enable, mcp_source, mcp_servers,
                 self.context['execute_ids'] = []
                 for tool_id in tool_ids:
                     tool = QuerySet(Tool).filter(id=tool_id).first()
-                    if not tool.is_active:
+                    if tool is None or tool.is_active is False:
                         continue
                     executor = ToolExecutor(CONFIG.get('SANDBOX'))
                     if tool.init_params is not None: