Text boxes take a string index from 0x5000 as a spinner's extra item's
description (kills_to_win_extra_descriptions). Custom Edition multiplayer
maps' display indices now run from 0x4000 to 0x6000 (8192 maps), so a
list of more than 4096 showed the next maps' names as kills-to-win
descriptions. The descriptions move to 0x7000, which custom_edition_maps.c
already keeps every map's display index below.