close Connection socket after server disconnect

[pawl]

This is similar to: redis/redis-py#1797

Currently, calibre/srv/loop.py's Connection.close() won't continue to close the socket if it encounters an OSError on socket.shutdown. An OSError can happen on socket.shutdown if the other side of the connection disconnected already. Not running socket.close prevents garbage collection from cleaning up the socket and will use more memory than necessary (maybe even causing a leak?).

This PR puts a separate try/except around socket.close and socket.shutdown to allow the socket to be closed after a failed shutdown.