Don't create unused OSError in Socket_Available.

runtime/bin/socket_patch.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.
 
 patch class RawServerSocket {
   /* patch */ static Future<RawServerSocket> bind(address,
                                                   int port,
                                                   {int backlog: 0,
                                                    bool v6Only: false}) {
     return _RawServerSocket.bind(address, port, backlog, v6Only);
@@ skipping 726 matching lines @@
         if (i == WRITE_EVENT) {
           writeAvailable = true;
           issueWriteEvent(delayed: false);
           continue;
         }
 
         if (i == READ_EVENT) {
           if (isListening) {
             available++;
           } else {
-            var avail = nativeAvailable();
-            if (avail is int) {
-              available = avail;
-            } else {
-              // Available failed. Mark socket as having data, to ensure read
-              // events, and thus reporting of this error.
-              available = 1;
-            }
+            available = nativeAvailable();
             issueReadEvent();
             continue;
           }
         }
 
         var handler = eventHandlers[i];
         if (i == DESTROYED_EVENT) {
           assert(isClosing);
           assert(!isClosed);
           isClosed = true;
@@ skipping 1162 matching lines @@
                        String address,
                        List<int> in_addr,
                        int port) {
   return new Datagram(
       data,
       new _InternetAddress(address, null, in_addr),
       port);
 }
 
 String _socketsStats() => _SocketsObservatory.toJSON();