If the user uses a keymap which defines a keysym for a certain keycode, defines
a keyboard shortcut using that symbol name, switches to another keymap (because
(s)he bought a new keyboard, for example) and logs in gnome-settings-daemon can
lock up the keyboard if the keysym is not defined in the new keymap. This
happens because XKeysymToKeycode returns 0 for the keyval in eggaccelerators.c.
There is a check for this in eggaccelerators.c but only in the "maybe it's a
keycode" case, not the "normal" case.

To reproduce the bug do the following:
- Use a keymap that doesn't have XF86Mail (for example) defined
- Use xmodmap to define a keycode for XF86Mail: xmodmap -e "keycode
SOME-KEY-CODE = XF86Mail"
- Open the Keyboard Shortcuts control panel
- Define a shortcut using the XF86Mail key you just defined
- Log out
- Log in - now XF86Mail is not defined anymore
- Keyboard is locked because gnome-settings-daemon translates XF86Mail to 0

Bug 135031 is related to this but doesn't fix this.

I've attached a trivial patch that checks if XKeysymToKeycode returns 0 and
marks it as bad_keyval as is done in the "maybe it's a keycode" case.