do_storage(): Unset highlighted item if list is empty
do_storage(): Unset highlighted item if list is empty

Check if the appointment panel contains any items and unset the
highlight counter if it doesn't. Not doing this resulted in core dumps
if the edit command was invoked after switching to a day without any
appointments/events.

Signed-off-by: Lukas Fleischer <af90e31281d8305af43dc616c5aaca3c7165f8a7@cryptocrack.de>

lfos/calcurse,lfos/calcurse,lfos/calcurse