mconf: handle keys in empty dialogs

When entering an empty dialog, using the movement keys resulted in
unexpected characters beeing displayed, other keys like "z" and "h"
did not work as expected.

This patch handles the movement keys as well as other keys, especially
"z", "h" and "/".

Signed-off-by: Dirk Gouders <dirk@gouders.net>
[yann.morin.1998@free.fr: keep lines <80 chars, so reorder test]
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>