Mixed mode mind runtime

Created by: gbasood

14:31:22 Runtime detected
type mismatch: /datum/mind (/datum/mind) += /datum/mind (/datum/mind) at mixed.dm:91
 proc name: pre setup (/datum/game_mode/mixed/pre_setup)
  source file: mixed.dm,91
  usr: null
  src: mixed (/datum/game_mode/mixed)
  call stack:
mixed (/datum/game_mode/mixed): pre setup()
/datum/controller/gameticker (/datum/controller/gameticker): setup()
/datum/controller/gameticker (/datum/controller/gameticker): pregame()
ticker (/datum/controller/process/ticker): setup()