when use ext-grid in one tree, other tree not use ext-grid has error on click

[yangjuncode]

Expected and Actual Behavior

should be no err

Steps to Reproduce the Problem

1. modify the demo/sample-3rd-grid-scrollbar.html
2. add a div and init a common tree without use ext

<div id="old-tree" style="width: 100%;height: 400px;"></div>

 $("#old-tree").fancytree({
      checkbox: true,
      source: {
        url: "https://cdn.jsdelivr.net/gh/mar10/assets@master/fancytree/ajax_101k.json",
        cache: true,
      },
  })

3. now click the old-tree, it will has error and tree click event can't got processing
   TypeError: vp is null jquery.fancytree.grid.js:620:15

Environment

• Browser type and version: firefox 70
• jQuery and jQuery UI versions:jQuery UI 1.12.1, jQuery 3.4.1
• Fancytree version: 2.33.0
  enabled/affected extensions:ext-grid

[yangjuncode]

this is my modify file
sample-3rd-grid-scrollbar.html.zip