fix disappearence of drag handler when using custom dragHandleSelector class with multiple elements

[dzeroone]

drag handler got hidden with usage of custom class selector.

drag handler element

<div class="custom-drag-handle">
  <button class="drag-handler-btn">Drag</button>
  <button class="add-action-btn">Add</button>
</div>

Editor config

new Editor({
  extensions: [
    GlobalDragHandle.configure({
        dragHandleSelector: ".custom-drag-handle", // default is undefined
    }),
  ],
})