Don't let ƒ break path names

[Iritscen]

Oni's standard Mac installation folder is named "Oni ƒ". We encourage players to remove this, but there's always going to be some who don't know better, and simply copy the folder from the CD-ROM and try to work with it that way.

See ​here for an example of what happens if someone tries to run the AEI with such a path.