WebSocket onClose not called for Netty

[U1F984]

After switching from jooby-undertow to jooby-netty, issue #3111 can be reproduced again with the lastest version. Using undertow with the latest version works correctly ("Connected" followed by "Disconnected").

If the socket is actively used by writing to it, there is an error:

java.lang.IllegalStateException: Attempt to send a message on closed web socket
	at io.jooby.internal.netty.NettyWebSocket.sendMessage(NettyWebSocket.java:178)
	at io.jooby.internal.netty.NettyWebSocket.send(NettyWebSocket.java:111)
	at io.jooby.WebSocket.send(WebSocket.java:205)
	at App$1$1$1.invoke(ServerMain.kt:16)
	at App$1$1$1.invoke(ServerMain.kt:13)
	at kotlin.concurrent.ThreadsKt$thread$thread$1.run(Thread.kt:30)

and the socket is marked as closed (isOpen returns true since the netty channel is dead), but the handleClose and so onClose callback is not invoked.

If I insert:

this.netty.ctx.channel().closeFuture().addListener(future -> handleClose(WebSocketCloseStatus.GOING_AWAY)); // or some other close status

into the constructor, the onClose is invoked successfully.

[jknack]

@U1F984 would you like to send a PR?