RoomBattle: Properly handle legacy config format
RoomBattle: Properly handle legacy config format

#8214 added code to handle Config.forcedpublicprefixes and convert it to Config.forcedprefixes, but it was buggy.

Zarel/Pokemon-Showdown,xfix/Pokemon-Showdown,Zarel/Pokemon-Showdown,xfix/Pokemon-Showdown,svivian/Pokemon-Showdown,svivian/Pokemon-Showdown,svivian/Pokemon-Showdown,xfix/Pokemon-Showdown,xfix/Pokemon-Showdown,Zarel/Pokemon-Showdown,svivian/Pokemon-Showdown,svivian/Pokemon-Showdown,xfix/Pokemon-Showdown