Fix demo not working anymore

js/demo.js

@@ -889,7 +889,10 @@ window.demoInterface = {
       }
     }
   },
+  didInit: false,
   init (screen) {
+    if (this.didInit) return
+    this.didInit = true
     this.terminal = new ScrollingTerminal(screen)
     this.shell = new DemoShell(this.terminal, true)
   }

js/term_conn.js

@@ -132,7 +132,7 @@ window.Conn = class TermConnection extends EventEmitter {
       if (typeof window.demoInterface === 'undefined') {
         alert('Demoing non-demo build!') // this will catch mistakes when deploying to the website
       } else {
-        demoInterface.init(screen)
+        demoInterface.init(this.screen)
         showPage()
       }
       return