how about to add condition that checks current page and total pages count?

gistfile1.js

//Insight.view.PagingGrid 

   storeListener : function(store) {
        var toolbar = this.down('pagingtoolbar');
        if ( toolbar ) {
	        var newVisible = (store.getTotalCount() > store.pageSize);
	        var oldVisible = toolbar.isVisible();
	        toolbar.setVisible(newVisible);
	        store.currentPage = (Math.ceil(store.getTotalCount()/store.pageSize) >= store.currentPage) ? store.currentPage : Math.ceil(store.getTotalCount()/store.pageSize);
	        if (oldVisible != newVisible) {
	            this.doComponentLayout();
	        }
        }
    }