Fix a crash on unexpected incoming DNS message during XoT xfer

Fix a crash on unexpected incoming DNS message during XoT xfer

This commit fixes a peculiar corner case in the client-side DoT code
because of which a crash could occur during a zone transfer. A junk
DNS message should be sent at the end of a zone transfer via TLS to
trigger the crash (abort).

This commit, hopefully, fixes that.

Also, this commit adds similar changes to the TCP DNS code, as it
shares the same origin and most of the logic.