handle_idx can't be < 0 because it's unsigned. Printing an ERR if the handle is out of range is probably ok, but I think crashing is better than just returning NULL.
I hoped that you would have thought otherwise about returning null. You might still get a crash at some point later, but the patch allows Warcraft III users to stay in the chat room much longer then one minute. I will make and resent an updated patch. Thanks for taking your time to review the patches.