lib/resolve: zonecut fetching error was fixed

Zone cut fetching error was fixed. If all the conditions are met:

1. NS for target record zone is located outside of target zone
2. NS belongs to secured zone
3. target record belongs to unsecured zone then zone for which NS belongs to is treated as insecured.

Reproducer:

1. Empty cache
2. dig us.dlink.com +dnssec
3. dig nominet.co.uk DS +dnssec -> AD flag is absent

mentioned in commit 4c81f488

merged