title: jqgrid getRowData returns null
body: <p>I have the code below:</p>
  
  <pre><code>$buttonoptions = array("#pager", 
      array(
          "caption" =&gt; "Select Product",
          "onClickButton" =&gt; "js: function() {
              var selr = jQuery('#grid').jqGrid('getGridParam', 'selrow');
              var kelr = jQuery('#grid').jqGrid('getRowData', 'product_cat_id');
              if(selr) { 
                  alert('grid.php?advice=' + selr + kelr); 
              } else {
                  alert('Please Select a Product!');
                  return false;
              }
          }"
      )
  );
  </code></pre>
  
  <p>I successfully got the row ID in the following way:</p>
  
  <pre><code>var selr = jQuery('#grid').jqGrid('getGridParam','selrow');
  </code></pre>
  
  <p>But couldn't get the data of the selected row's <code>product_cat_id</code> column.</p>
  
  <p>What is wrong?</p>