title: Struts2 - datepicker client-side validation returns same error message twice
body: <p>I use a struts2 form with datepicker:</p>
  
  <pre><code>&lt;s:form action="%{#parameters.myAction}" namespace="/" method="post" name="myForm" enctype="multipart/form-data" focusElement="dealTitleId" validate="true"&gt;
  ...
  &lt;sj:datepicker name="dealDisplayEnd" required="true" key="dealDisplayEnd-label" displayFormat="dd-mm-yy" readonly="true" minDate="0"/&gt;
  </code></pre>
  
  <p>Please note the <code>validate="true"</code> option which enables the client-side validation (I need this to prevent losing some other information about file upload when some error occurs).</p>
  
  <p>Then also created the XML for it:</p>
  
  <pre><code>&lt;field name="dealDisplayEnd"&gt;
          &lt;field-validator type="required"&gt;
               &lt;message key="error.dealDisplayEnd.empty"/&gt;
          &lt;/field-validator&gt;
    &lt;/field&gt;
  </code></pre>
  
  <p>Everything works fine, except that the error is repeated twice:</p>
  
  <p><img src="https://i.stack.imgur.com/1onGK.png" alt="Error is shown twice"></p>
  
  <p>Looking at the web page source, I see that the validation script is generated twice:</p>
  
  <pre><code> // field name: dealDisplayEnd
          // validator name: required
          if (form.elements['dealDisplayEnd']) {
              field = form.elements['dealDisplayEnd'];
              var error = "Deal display end date must be provided!";
              if (field.value == "") {
                  addError(field, error);
                  errors = true;
  
              }
          }
          // field name: dealDisplayEnd
          // validator name: required
          if (form.elements['dealDisplayEnd']) {
              field = form.elements['dealDisplayEnd'];
              var error = "Deal display end date must be provided!";
              if (field.value == "") {
                  addError(field, error);
                  errors = true;
  
              }
          }
  </code></pre>
  
  <p>Is this a struts2 bug? Or am I doing something wrong? Is it because I'm using datepicker and client-side validation? I'm using struts2-core-2.3.4.jar and struts2-jquery-plugin-3.3.3.jar.
  Is there an easy way for me to patch (I could not locate the place where this is generated)?</p>
  
  <p>Thanks.</p>