title: Selected field is blank when fetches a Backbone collection with Backbone-forms
body: <p>I use <a href="https://github.com/powmedia/backbone-forms" rel="nofollow">Backbone-forms</a> for populate a Model. I have a select field with a backbone collection as options in the scheme. When this collection is empty, backbone-forms does a fetch, but the html of select appears blank. </p>
  
  <p>When the collection is non empty always takes first option as value. </p>
  
  <p>I would like the first time, when the collection is empty, it will shows the first value by default too.</p>
  
  <pre><code>class foo extends Backbone.Model
    schema:
      tag:
       type: 'select'
       options: new App.Collections.Tags
  </code></pre>