I think this is a good change...
Actually, it's not. sizeof (char *) == 4... That commit is wrong.
but that's assuming 63 chari in ISO-Latin or UTF-8
That's not what this commit is for. That commit is merely to ensure that you don't overrun the 64 bytes buffer on copy, something Asus failed to do, as they were blindly taking the hostname from dnsmasq's lease file, and copying it to a static sized buffer. Truncating a hostname to 63 characters (who the hell has a hostname THAT long anyway?) is perfectly fine, especially since this is strictly for display purposes on the webui.
Also, it's strictly a hostname, it's not a FQDN.