Gardening: Fix previous fix

tests/standalone/io/named_pipe_script_test.dart

 // Copyright (c) 2016, 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.
 // Testing file input stream, VM-only, standalone test.
 
 import "dart:convert";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 main() async {
   asyncStart();
   // Reading a script from a named pipe is only supported on Linux and MacOS.
   if (!Platform.isLinux && !Platform.isMacOS) {
     print("This test is only supported on Linux and MacOS.");
+    asyncEnd();
     return;
   }
 
   final String script = 'main() { print("Hello, World!"); }';
   final String stdinPipePath = '/dev/fd/0';
 
   // If there's no file system access to the pipe, then we can't do a meaningful
   // test.
   if (!await (new File(stdinPipePath).exists())) {
     print("Couldn't find $stdinPipePath.");
+    asyncEnd();
     return;
   }
 
   StringBuffer output = new StringBuffer();
   Process process =
       await Process.start(Platform.executable, ['--checked', stdinPipePath]);
   bool stdinWriteFailed = false;
   process.stdout.transform(UTF8.decoder).listen(output.write);
   process.stderr.transform(UTF8.decoder).listen((data) {
     if (!stdinWriteFailed) {
@@ skipping 10 matching lines @@
   process.stdin.writeln(script);
   process.stdin.close();
 
   int status = await process.exitCode;
   if (!stdinWriteFailed) {
     Expect.equals(0, status);
     Expect.equals("Hello, World!\n", output.toString());
   }
   asyncEnd();
 }