部分xmind版本复制的时候前端报错，无响应

还有复制xmind内容到页面的时候 这里有个空索引问题 这里是按照\t 进行索引判断的。 有些xmind版本中间会漏一层 导致这里抛异常。目前没有好的解决方案. 只能在clipboard.js外层事件层做一个错误提醒了

Start at the outer event layer around clipboard.js and reproduce the error by copying XMind content with a missing tab-index layer. The issue describes the desired outcome as showing an error reminder instead of allowing the page to become unresponsive; no specific source file or test is named.

Written by the indexing model from the issue text.