[CVE-2026-3119] sec: usr: Prevent a crash in code processing queries containing a...

The :iscman:`named` process could terminate unexpectedly when
processing a correctly signed query containing a TKEY record.
This has been fixed.

ISC would like to thank Vitaly Simonovich for bringing this
vulnerability to our attention.

Closes isc-projects/bind9#5748

Merge branch '5748-security-tkey-delete-bug-fix' into 'v9.21.20-release'

See merge request isc-private/bind9!922