Fixed bug with RpcConnect shutdown method when socket is already closed.

sjrpc/core/rpcconnection.py

@@ -350,7 +350,10 @@ class RpcConnection(object):
         :type callback: :class:`str` or callable or None
         '''
 
-        self._sock.close()
+        try:
+            self._sock.close()
+        except socket.error as err:
+            logging.warning('Error while socket close: %s.', err)
 
         # Release all running calls from this connection:
         for call in self._calls.values():