title: Bootstrap Selectpicker - noneResultsText is not working with optgroup
body: <p>I am using bootstrap selectpicker to make the custom select box. Problem is noneResultsText is not coming with optgroup, when i am removing optgroup noneResultsText is working fine. Not sure what would be the solution.</p>
  
  <p>HTML:</p>
  
  <pre><code>&lt;select class="selectpicker" data-live-search="true" &gt;
      &lt;optgroup label="Picnic"&gt;
         &lt;option&gt;Alabama&lt;/option&gt;
         &lt;option&gt;Alaska &lt;/option&gt;
         &lt;option&gt;Arizona &lt;/option&gt;    
      &lt;/optgroup&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>JS:</p>
  
  <pre><code>$('.selectpicker').selectpicker({
             noneResultsText: 'I found no results'
        });
  </code></pre>
  
  <p>Working example :<a href="http://jsfiddle.net/9abm0hhy/24/" rel="nofollow">http://jsfiddle.net/9abm0hhy/24/</a></p>