Only close the sync socket if it is non-NULL. This fixes...

ppapi/shared_impl/audio_impl.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/shared_impl/audio_impl.h"
 
 #include "base/logging.h"
 
 namespace pp {
 namespace shared_impl {
 
 AudioImpl::AudioImpl()
     : playing_(false),
       shared_memory_size_(0),
       callback_(NULL),
       user_data_(NULL) {
 }
 
 AudioImpl::~AudioImpl() {
   // Closing the socket causes the thread to exit - wait for it.
-  socket_->Close();
+  if (socket_.get())
+    socket_->Close();
   if (audio_thread_.get()) {
     audio_thread_->Join();
     audio_thread_.reset();
   }
 }
 
 void AudioImpl::SetCallback(PPB_Audio_Callback callback, void* user_data) {
   callback_ = callback;
   user_data_ = user_data;
 }
@@ skipping 55 matching lines @@
       pending_data >= 0) {
     // Exit the thread on pause.
     if (pending_data < 0)
       return;
     callback_(buffer, shared_memory_size_, user_data_);
   }
 }
 
 }  // namespace shared_impl
 }  // namespace pp