NFD

Steps to reproduce:

1. start ndnpingserver on the router
2. create a web application with NDN-JS that sends ping Interests continuously at 200ms interval
3. run the web application on an Android phone, connect to the router over a high-latency (200ms or more) link
4. hit REFRESH button on the phone browser

Expected: NFD destroys the face

Actual: with high probability, NFD crashes with terminate called after throwing an instance of 'boost::system::error_code'

More information:

• gdb stack trace reveals the crash happens in nfd::WebSocketFace::sendData.
• The log message immediately before the crash is 1404449150.332705 INFO: [FaceTable] Removed face id=23 remote=wsclient://180.158.23.39:44199 local=ws://[::]:9696, which indicates the face is already closed. However, PIT Downstream Record contains a reference to the face, so sendData is still called.