device-manager: Actually fall back to reading from tty if no xkb layout specified
Commit 7fcfcdf2d63025151a160f7948ee7406f0f16843 tried to fall back to reading from a tty if no xkb layout was specified, but neglected to actually check if no xkb layout was specified and force fall back to reading from a tty in that case.
This commit changes device manager to actually disable reading from /dev/input if the user doesn't specify a layout to use in vconsole.conf.
Closes #199 (closed)