kconfig/mconf.c: revision of curses initialization.

Since commit d0e1e09568 initscr() is called twice in mconf.

Do it only in init_dialog() in util.c and there also save the
cursor position for the signal handler in mconf.c.

Signed-off-by: Dirk Gouders <gouders@et.bocholt.fh-gelsenkirchen.de>
Signed-off-by: Michal Marek <mmarek@suse.cz>