title: KendoGrid Validation for a field doesn't get called on grid column sort/filter
body: <p><code>Validation</code> used  for a field  in <code>KendoGrid</code> works fine on currently being edited cell when I try to select other cell.But It <code>doesn't work</code> when I try to sort any column or use filter.
  How can I enforce validation as the way normal focusout event works to any HTML element?</p>
  
  <p>Code used in datasource </p>
  
  <pre><code>var mainDataSource={
              data :listJson   
              ,type:"json"
              ,batch:true
              ,schema: {
                  model: { 
                      id: "Port_ID" 
                      ,fields:{
                              Port_ID:{type: "string",editable:false,nullable:false}
                              ,Slot1:{type:"number",editable:false}
                              ,Slot2:{type:"number",editable:false}
                              ,Type1:{type: "string",editable:true}
                              ,Type2:{type: "string",editable:false}
                              ,IsHFL:{type:"boolean",editable:false}
                             Project:{
                                  type:"string"
                                  ,editable:true
                                  ,validation: {
                                      custom: function(input) {
                                          if(input.val()=="") {//to be added further
                                              input.attr("data-custom-msg", "Message");
                                              return false;
                                          }
                                          else
                                              return true;
                                      }
                                  }
                              }
  
                             ,Used_For:{ type: "string",editable:true}
                            ,Start_Date:{type:"date",editable:true}
  
                             }
                  }
              }
      };
  </code></pre>