Correct me if I am wrong but I believe the existing function is working perfectly as coded and intended according to the following:
[Feature] Add unapproved topic icon for moderators on forum list. (Bug #46865)
So what is there to fix? This seems like another bogus bug report to me. The only time you are supposed to be presented with an unapproved icon on the forum index is if there are unapproved topics not unapproved posts. I would not like to see the forum index page littered with icons for each and every unapproved post that isn't a topic starter. It is currently a nice feature to have only new topics needing attention flagged on the index without having to go into the MCP to see if there are any and I love the fact that the icon links directly to the 'Topics awaiting approval' tab of the MCP. Where would the icon redirect if a forum had both unapproved topics and unapproved replies? I hope that you don't change the current behavior but if you do you should provide an easy way (GUI based) to disable the inclusion of non-topic posts as a trigger for the icon.