cmenu: redraw the current menu after exiting the keys_handler

cmenu: redraw the current menu after exiting the keys_handler

After exiting the keys_handler, reset_ui() is not enough since it
only resets the status line and title. The current menu needs to be redrawn.

Note: only a submenu will be redrawn, not its parents. This means that not
all the UI will be displayed after exiting the handler if invoked from whithin a
submenu. We have already this problem nowadays when exiting a submenu
of a submenu. The root parent is not redrawn, leading to some ugly states
(the background color overrides part of the root menu).
This will be fixed when we implement a real hierarchy (each submenu having
access to its parents).

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>