fix: stdio mcp schema parse error

Author: zgqgit

src/backend/bisheng/api/services/tool.py

@@ -87,7 +87,7 @@ async def parse_mcp_schema(self, file_content: str) -> GptsToolsTypeRead:
         for key, value in mcp_servers.items():
             # 解析mcp服务配置
             tool_type = GptsToolsTypeRead(name=value.get('name', ''),
-                                          server_host=value.get('url'),
+                                          server_host=value.get('url', ''),
                                           description=value.get('description', ''),
                                           is_preset=ToolPresetType.MCP.value,
                                           openapi_schema=file_content,