title: extjs store collect not working when data fetched through service call
body: <p>I am using ext4. I have to populate four combo box with distinct value using data in store.
  But while using collect method on store it gives empty array. It works when I have static data in store but it does not work when I fetch data by using proxy in store.</p>
  
  <pre><code>    /* inside view */
      initComponent: function() {
              console.log('inside menu Panel ');
              var me = this;
              var filterCriteriaStore = Ext.create('ITChart.store.StoreForMenu');
              Ext.applyIf(me, {
                  defaults:{
                      margin:'20 40 20 20'
                  },
                  items: [
                          {
                              xtype: 'combo',
                              id: 'territory',
                              store: filterCriteriaStore.collect('territory'),
                              displayField: 'territory',
                              valueField:'territory',
                              maxWidth:'100',
                              margin: '20 40 20 0',
                              value: 'ABC'
                          },
                          {
                              xtype: 'combo',
                              id: 'content',
                              store: filterCriteriaStore.collect('content'),
                              displayField: 'content',
                              valueField:'content',
                              maxWidth:'100',
                              value: 'XYZ'
                          }
                          ]
  
              });
              me.callParent(arguments);
          }
  
      /* not working */
      /* inside store */
      proxy: {
              type: 'ajax',
              url : 'http://localhost:8080/ServiceName/getFilterCriteriaExt',
              reader: {
                  type: 'json',
                  root: 'responseDTO'
              }/*,
              headers: {
                  'Content-Type': 'application/json; charset=utf-8; Cache-Control: no-cache'
              }*/
              //actionMethods: 'POST'
          },
  
      /* working */
      /* inside store */
      data : [
  {"content":"XYZ","type":"Song","territory":"ABC","payment":"Paid","errorCode":""},{"content":"Music","type":"Album","territory":"ABC","payment":"Paid","errorCode":""},{"content":"XYZ","type":"Song","territory":"IND","payment":"Paid","errorCode":""},
  {"content":"Music","type":"Album","territory":"ABC","payment":"Paid","errorCode":""},
  {"content":"Movie","type":"Song","territory":"CHINA","payment":"NotPaid","errorCode":""},
  {"content":"Music","type":"Song","territory":"IND","payment":"NotPaid","errorCode":""}
      ]
  </code></pre>