joomla onContentBeforeSave ..继续将readmore div添加到文本中

Trying to make same changes to article using a plugin just before saving. Joomla! keep adding readmore div to text.

class PlgContentEditArti extends JPlugin
{
    function onContentBeforeSave($context, $article, $isNew)
    {
        if($context == "com_content.article")
        {   
        $article->fulltext = "hi";

        }

        return true;
    }
}

Output

<hr id="system-readmore" />
<p>hi</p>