The joystick can't be disabled

Hi,

Even when setting the joystick enable option to false in the settings file, the joystick is enabled in game and saved back to yes in the settings file.

Unfortunately, due to a ghost joystick existing on debian, this makes playing solarus impossible. EDIT: It's not a blocker for me as I simply disable the joystick key handling code, but could be for others, (just in case.)