title: Flutter: local_auth sometime do not present authentication dialog
body: <p>I am using the flutter plugin local_auth 0.6.0+1. I am testing a basic implementation and I experience a strange behaviour in showing the auth dialog. I basically call the <code>checkIfCanAccessWithBiometric</code> method by pressing a button. Some time the dialog pops up immediately, some other time it takes a while, some other time does not pop up and it pops up only if I touch the screen. How can I resolve this issue?? thanks </p>
  
  <pre><code>  void checkIfCanAccessWithBiometric() async {
      bool didAuthenticate = await _localAuth.authenticateWithBiometrics(
          localizedReason: 'Please authenticate to login', 
          stickyAuth: true);
      print(didAuthenticate);
    }
  </code></pre>