Forbid the asterisk (*) single character domains on non-leaf level in the master zones

Currently, the sub.*.example.com is a valid and legal domain name. But not everything that's legal is right and this is a perfect example, as the domain in question is not a wildcard domain name covering sub.<anything>.example.com, but a single domain name sub.*.example.com where * is literal asterisk character. Remember that * has no special meaning in the QNAME, it is only processed as * when loading the zone files.