#1 can't change video settings in-game

[Wart]

The video settings (fullscreen, background,
alpha-blend, effects) can't be changed via the settings
menu while the game is running.

Steps to reproduce:

1) start abe
2) Select "Settings" from the main menu
3) Press the down arrow until the token is next to
"background"
4) Press <space> to toggle the background option

Actual results:
Nothing happens.

Expected results:
The option changes from "On" to "Off"

Note:
The problem is the isEnabled() function in src/Menu.c.
The default return value is '0', unless an audio
option is selected. Changing the default return value
to '1' fixes the problem.

The attached patch against version 1.1 contains the fix.