Extras level select fix

This should fix a bug (introduced by !2081 (merged), whoops) where if you loaded a level from the Extras menu's level select (if unlocked), then opened up the pause menu, entered level select there and loaded another level, it doesn't work and the console gives a "Couldn't read file srb2sav0.ssg" message.

(Technically, the issue is that starting up a game from Extras menu means you have no save slot, so the pause menu level select tries and fails to load a save data file for slot "0" which doesn't exist. The solution here is to start a new game from scratch, but keeping your current skin.)