GUACAMOLE-623: Kill connection if libwebsockets is destroying the underlying WebSocket.

Older versions of libwebsockets will not necessarily invoke close events
under all circumstances, and will instead sometimes summarily destroy
the WebSocket. Thankfully there is another event for that, and newer
versions of libwebsockets continue to define that event. We can hook
into both to handle disconnect.

src/protocols/kubernetes/kubernetes.c

@@ -120,6 +120,7 @@ static int guac_kubernetes_lws_callback(struct lws* wsi,
 #endif
 
         /* Connection closed */
+        case LWS_CALLBACK_WSI_DESTROY:
         case LWS_CALLBACK_CLOSED:
             guac_client_stop(client);
             guac_client_log(client, GUAC_LOG_DEBUG, "WebSocket connection to "