title: RefreshIndicator not working combined with extendBodyBehindAppBar true
body: <p>I have this issue that the RefreshIndicator doesn't work properly combined with the Scaffold property extendBodyBehindAppBar: true.</p>
  
  <p>Here is the code snippet that causes the error. In total the RefreshIndicator is pulled down from above the status bar and therefore the indicator has a long way till being dragged down to the visible body part. If the user drags only half the way the indicator can also be behind the app bar which is for sure not an intended behaviour. Is there a way to have the <code>RefreshIndicator</code> together with the Scaffold property <code>extendBodyBehindAppBar: true</code>?</p>
  
  <pre><code>Scaffold(
      extendBodyBehindAppBar: true, // true causes a layout error
      appBar: AppBar(...),
      body: RefreshIndicator( 
        onRefresh: () {
          // some logic
        },
        child: ListView(
          children: &lt;Widget&gt;[
  </code></pre>