Pure CSS Star Rating - Enforce Non-Zero Result

I've been using the pure CSS example found here: http://www.danielkeithjones.com/Articles/Web_Development/Pure_CSS_5_Star_Rating_System_with_Radios/

But I cannot figure out how to prevent the form from submitting when there are zero stars selected (which it initiates as). Basically: if the star-based question is required I want to say "it has to be 1-5 stars" but since the default is 0 JavaScript seems to ALWAYS think it's zero until the form saves.

What am I missing?

Here is the JavaScript I'm using:

    // Check radio buttons
    jQuery("input.input-required:radio").each(function() {
        var name = jQuery(this).attr("name");
        var group = jQuery("input:radio[name='"+name+"']");
        radio_groups[name] = false;
        radio_groups[name] = (radio_groups[name] == true) || (group.is(":checked") && group.val() != "0 stars");
    });
    for(var key in radio_groups) {
        if(radio_groups.hasOwnProperty(key) && radio_groups[key] == false) {
            alert("This question is required");
            return false;
        }
    }

I'm not sure what your HTML looks but with the following html:

<form>
  <input type="radio" name="testing" value="0 stars" class="input-required" checked>
  <input type="radio" name="testing" value="1 stars" class="input-required">
  <input type="radio" name="testing" value="2 stars" class="input-required">
  <input type="radio" name="testing" value="3 stars" class="input-required">
  <input type="radio" name="testing" value="4 stars" class="input-required">
  <input type="radio" name="testing" value="5 stars" class="input-required">
  <button type="submit">Submit</button>
</form>

and the following js:

$('form').on('submit', function(){
    var valid=true;
    $('input.input-required:radio').each(function(){
        if (valid) {
          var name = this.name,
              value = $('input[name="' + name + '"]:checked').val();
          if (value == "0 stars"){
            alert('This question is required');
            valid=false;
          }
        }
    });
    return valid;
});

It works.