validator: avoid clearing EDE if request didn't actually fail
@vcunat The issue we were discussing yesterday in chat, that EDEs get cleared if a query fails (RRSIGs for A have expired in this case), but a subsequent query (AAAA for the NS) succeeds, and then the request finally SERVFAILs, in resolver, because it realises all servers are (DNSSEC-)broken (the query was: A rrsig-exp-a.extended-dns-errors.com
).