Fix errors in dart:io tests found by the analyzer

tests/standalone/io/file_non_ascii_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:io';
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 main() {
@@ skipping 32 matching lines @@
                     });
                   });
                 });
               });
             });
           });
         });
       });
     });
   }).catchError((e) {
-    port.close();
     Expect.fail("File not found");
   });
 }