Fix the link to ncurses patch download in macos installer build script (GH-20421)

Reason: the link `ftp://invisible-island.net/ncurses//5.9/ncurses-5.9-20120616-patch.sh.bz2` is dead, which prevents `Mac/BuildScript/build-installer.py` from completing. Looks like the host of the FTP server was changed to `ftp.invisible-island.net`, thus this proposal.

Signed-off-by: oleg.hoefling <oleg.hoefling@gmail.com>