kconfig: check ncursesw headers first in check-lxdialog

Commit 8c41e5e3 added a check for
ncursesw/curses.h for the case where ncurses and ncursesw are build
separately but only one is installed.  But if both are installed,
the headers ncurses/curses.h and ncursesw/curses.h differ, and since
libncursesw will be found first, so should ncursesw/curses.h.

Signed-off-by: Yaakov Selkowitz <yselkowitz@users.sourceforge.net>
Signed-off-by: Michal Marek <mmarek@suse.cz>