title: x-editable sends empty field although "savenochange" is set to true
body: <p>I have multiple fields being edited with x-editable, saving them all at once after a submit button was clicked, based on this example: </p>
  
  <p><a href="https://vitalets.github.io/x-editable/docs.html#newrecord" rel="nofollow">https://vitalets.github.io/x-editable/docs.html#newrecord</a></p>
  
  <p>This is the code handling the saving process:</p>
  
  <pre><code>    $('.lpeditable').editable({
        url: "/post",
        savenochange: true
      });
  
      $('#save-btn').click(function() {
        $('.lpeditable').editable('submit', {
          url: '/post',
          data: {
            sub: $('#_sub').val()
          },
          ajaxOptions: {
             dataType: 'json'
          },
          success: function(data, config) {
            console.log("Success:");
            console.log(data);
          },
          error: function(errors){
            console.log(errors);
            if(errors.responseText == "missing-sub"){
              console.log("Sub missing!!");
            }
          }
        });
      });
  </code></pre>
  
  <p>On post it gets JSON encoded and saved into a database, when the page is loaded it gets read from the database and the page gets updated with following js code:</p>
  
  <pre><code>&lt;script&gt;
  $(document).ready(function(){
    $('.lpeditable').each(function(e) {
        var dname = $(this).attr('data-name');
        var fields = &lt;?php if(!empty($fields)) { echo json_encode($fields); } ?&gt;;
  
        if(fields !== undefined || fields !== null){
          if(fields[dname].length &gt; 0){
            $(this).html(fields[dname]);
            $(this).removeClass('editable-empty');
          }
        }
        else {
          //
        }
    });
  });
  &lt;/script&gt;
  </code></pre>
  
  <p>Everything seems to work fine, except if I edit only one value it sends an empty string ("") for every other value. Savenochange seems to have no effect at all.</p>
  
  <p>I also tried this approach:</p>
  
  <pre><code> $('.lpeditable').editable({
        url: "/post",
        savenochange: true
      }).on('save', function(){
        var dataJ = {};
        $('.lpeditable').each(function(){
          var currAttr = $(this).attr('data-name');
          dataJ[currAttr] = $(this).editable('getValue');
        });
        $.ajax({
          url:"/post",
          data: dataJ,
          sub: $('#_sub').val(),
        })
      });
  </code></pre>
  
  <p>But it sends this:</p>
  
  <pre><code>{"headline":{"headline":""},"headline2":{"headline2":""}}
  </code></pre>
  
  <p>So it seems like</p>
  
  <pre><code>$(this).editable('getValue');
  </code></pre>
  
  <p>Is not returning anything, it is empty aswell.</p>
  
  <p>Any way to not overwrite unchanged values with empty ones?</p>