Huh, well that's embarrassing. It looks like it's still in there too. I googled the man page but I guess I saw an older version. I might submit a patch if I find time. It should really be something like this:

    if (n > 0) {
        strncpy(buf, str, n - 1);
        buf[n - 1] = '\0';
    }

Of course, the error isn't super huge considering if you're using a zero-length buffer as a null-terminated string you're going to have other problems. But they still do check for 0, so IMO it's worth correcting.