fix a bug that happens when a thread is deleted
fix a bug that happens when a thread is deleted

HuijiWiki/bootstrap-mediawiki,HuijiWiki/bootstrap-mediawiki,HuijiWiki/bootstrap-mediawiki,HuijiWiki/bootstrap-mediawiki,HuijiWiki/bootstrap-mediawiki,HuijiWiki/bootstrap-mediawiki