Make sure the socket unsubscribes on error, so we don't get race conditions between an error and an…

sdk/lib/io/io_stream_consumer.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 /**
  * Helper class to wrap a [StreamConsumer<List<int>, T>] and provide utility
  * functions for writing to the StreamConsumer directly. The [IOSink]
  * buffers the input given by [add] and [addString] and will delay a [consume]
@@ skipping 140 matching lines @@
           } else {
             _controller.close();
           }
         },
         onError: _controller.signalError);
     if (_paused) _pause();
     if (unbind) {
       _pipeFuture.catchError((error) {
         if (unbindCompleter != null) {
           unbindCompleter.completeError(error);
+          unbindCompleter = null;
         }
       });
       return unbindCompleter.future;
     } else {
       return _pipeFuture;
     }
   }
 }