lib/client: throw error in send if disconnected

lib/client.js

@@ -341,6 +341,9 @@ export default class Client extends EventTarget {
 	}
 
 	send(msg) {
+		if (!this.ws) {
+			throw new Error("Failed to send IRC message " + msg.command + ": socket is closed");
+		}
 		this.ws.send(irc.formatMessage(msg));
 		console.log("Sent:", msg);
 	}