title: Show p:dialog using oncomplete only if custom validation in action was passed
body: <p>I have a problem showing a dialog when I try to do a test in the <code>oncomplete</code> attribute.<br>
  But when I refresh the page it worked fine, and I have to refresh on each change of the variable in the backing bean.
  Even if I show the dialog without test it worked to.
  The problem is in debug mode. JSF doesn't call <code>get</code> when I test after the action was invoked.</p>
  
  <pre><code>&lt;p:commandButton value="#{msg.LABEL_ADD}"
                   action="#{axeBean.calculer}"
                   style="width:100px;"
                   update="msgs"
                   oncomplete="if(#{axeBean.formvalide})  PF('dialog').show()" /&gt;
  </code></pre>
  
  <p><code>formvalide</code> is a <code>boolean</code>.</p>
  
  <p>How can I solve this issue?</p>