dnsdbq check if -V summarize with -O

[reedjc]

Have dnsdbq check if -V summarize with -O to not send offset on to server since will get 416 error:

libcurl: Error: offset not allowed for this type of query

So consider failing at dnsdbq client first (don't send query).

[vixie]

this required small restructuring in validate_verb().