Hopefully fix that sometimes key is not accepted

Most likely this is a race condition...

lib/main.dart

@@ -96,6 +96,11 @@ class _MyHomePageState extends State<MyHomePage> {
       client = null;
     }
 
+    if (key == '') {
+      // make sure, the key is loaded
+      await obtainKeyPair();
+    }
+
     setState(() {
       _output = null;
     });