editors/hexcurse: fix build on 14.1

hexcurse.c:237:30: error: 'snprintf' will always be truncated; specified size is 1, but format string expands to at least 2 [-Werror,-Wformat-truncation]

237 |         min_address_length = snprintf(buffer, 1, "%jd", (intmax_t)len);
    |                              ^

1 error generated.