Handle case when socket not opened

If the socket is not already opened, listen for ‘open’ event before sending the `outputDone` data.

lib/modules/webserver/server.js

@@ -42,8 +42,13 @@ class Server {
     this.app.ws('/', function(ws, _req) {
       self.events.on('outputDone', () => {
         if (ws.readyState === WEB_SOCKET_STATE_OPEN) {
-          ws.send('outputDone');
+          return ws.send('outputDone');
         }
+        // if the socket wasn't yet opened, listen for the 'open' event,
+        // then send the 'outputDone' data
+        ws.addEventListener('open', _event => {
+          ws.send('outputDone');
+        });
       });
     });