title: ExtJs bufferedrenderer plugin and locked column conflict
body: <p>I need to lock some columns in grid. Here is my code with configuration of grid:</p>
  
  <pre><code>Ext.define('Crm.view.tables.baseTable', {
  extend: 'Ext.grid.Panel',
  alias : 'widget.baseTable',
  columnLines: true,
  initComponent: function(){
  var that = this;
  var $this = that;
  
  this.selType = 'checkboxmodel',
  this.selModel = {
      allowDeselect: true,
      mode: "MULTI"
  };
  
  this.plugins = [
      new Ext.grid.plugin.CellEditing({
              clicksToEdit: 2
          }),
          {
              ptype: 'bufferedrenderer',
              numFromEdge: 8,
              trailingBufferZone: 10,
              leadingBufferZone: 10
          }
  ];
  
  var filters = {
          ftype: 'filters',
          encode: true,
          local: true
  
      };
  
  this.features = [filters];
  
      var columns = [
          new Ext.grid.RowNumberer(),
          {
              header   : 'ID',
              dataIndex: 'id',
              locked   : true,
              filterable: true,
              width    : 30
          },{
              header  : 'ФИО',
              width   : 100,
              dataIndex: 'name',
              filterable: true,
              filter: {
                  type: 'string'
              },
              editor: 'textfield'
          },{
              header   : 'Телефон',
              dataIndex: 'phone',
              filterable: true,
              width    : 75,
              editor: 'textfield'
          },{
              header   : 'Email',
              dataIndex: 'email',
              filterable: true,
              width    : 90,
              editor: 'textfield'
          }
      ];
  
  this.columns = columns
  
  var tbar = [{
          text: 'Обновить',
          handler: function(){
              $this.getStore().reload();
          }
  },'-',{
      text: 'Очистить фильтр',
      handler: function () {
          that.filters.clearFilters();
      }
  },'-']
  
  this.tbar = tbar;
  
  this.callParent();
  
  }
  });
  </code></pre>
  
  <p>But I get an error:</p>
  
  <pre><code>Uncaught TypeError: Cannot call method 'on' of undefined ext-all-debug.js:115013
  </code></pre>
  
  <p>When I remove <code>bufferedrenderer</code> plugin from config, the locked column
  works. What is the problem? Thanks for answers!</p>