In September 2017 I moved loading arenas.txt/*.arena files from entering
start server menu to at startup to fix running out of memory in Team Arena
UI after opening the start server menu several times.
However, Team Arena completely replaces the uiInfo.mapList array when
switching between single player and start server menus. So after my
change, entering single player and then entering start server would only
display single player maps. It caused SP endofgame menu to use MP map
list for replay/next map since arenas were loaded after gameinfo.txt.
Continue loading arena info at start up to avoid reallocating arena info
but move setting up uiInfo.mapList to when entering the start server
menu.