Fix crash when keybindings are disabled that we want to show in the status bar

If a keybinding that we want to display in the options bar was set to <disabled>
by the user, in pre-0.62 versions we would still display the command, but with
no keybinding. This was arguably not very useful before, but now it actually
crashes because we would now try to display the first key of the slice of
configured keys (crash introduced in 3d18ee8f91c7). Fix the crash by not showing
those commands at all.