Modify empty zone conflicts under exclusive mode
    
    Does not accept new request when exclusive mode is active. Zone table
    can be modified even after main fwd entries have been added. Ensure
    empty zones handling keeps exclusive mode active.
    
    Exclusive mode were mentioned as the only protection it had by bind
    maintainer:
    https://gitlab.isc.org/isc-projects/bind9/-/merge_requests/6637#note_308928