static/ext/src/toolbar/Paging.js
function(){
        var me = this,
            total = me.getPageData().pageCount,
            next = me.store.currentPage + 1;

        if (next <= total) {
            if (me.fireEvent('beforechange', me, next) !== false) {
                me.store.nextPage();
            }
        }
    }
function(){
        var me = this,
            total = me.getPageData().pageCount,
            next = me.store.currentPage + 1;

        if (next <= total) {
            if (me.fireEvent('beforechange', me, next) !== false) {
                me.store.nextPage();
            }
        }
    }
Move to the next page, has the same effect as clicking the 'next' button.