these are short, and only used in FindDNSSECContext, so it'd make more sense
to enclose them there.
Other cleanups:
- also made FindDNSSECContext::isNSEC/isNSEC3 private as they now don't need
  to be called outside the class
- removed isInited(); simpy doesn't see the need for it as a separate method
- simplified the code logic of getResultFlag()