[FIX] base_import: error message

During the import of a file, if the connection is closed (timeout,
server shutdown...), a traceback appears.

This is because `error.data.arguments` is not defined in this case.

opw-682104

addons/base_import/static/src/js/import.js

@@ -411,7 +411,7 @@ var DataImport = Widget.extend(ControlPanelMixin, {
                 return $.when([{
                     type: 'error',
                     record: false,
-                    message: error.data.arguments[1],
+                    message: error.data.arguments && error.data.arguments[1] || error.message,
                 }]);
             }) ;
     },