ui/curses: Fix monitor color with -curses when 256 colors

If TERM=xterm-256color, COLOR_PAIRS==256 and monitor passes chtype
like 0x74xx. Then, the code uses uninitialized color pair. As result,
monitor uses black for both of fg and bg color, i.e. terminal is
filled by black.

To fix, this initialize above than 64 with default color (fg=white,bg=black).

FIXME: on 256 color, curses may be possible better vga color emulation.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
