this test adds a record with empty non-terminal nodes above it. this
has also been observed to trigger the crash in NSEC3 zones.
NOTE: the test currently fails, because while there is no crash, the
query results are not as expected. when we add a node below an ENT,
receive_secure_serial() gets DNS_R_PARTIALMATCH, and the signed
zone is never updated. this is not a regression from fixing the
crash bug; it's a separate inline-signing bug.
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