Strange response to mangled requests

[Stephane Bortzmeyer]

On Thu, Apr 02, 2020 at 04:48:38PM +0200,
 Wouter Wijngaards via Unbound-users <unbound-users at lists.nlnetlabs.nl> wrote 
 a message of 69 lines which said:

> probably depends on the 'use case' of formerr inputs, but I do not
> know of any.

Here, the use case was to test DoT servers (the script I sent uses UDP
but DoT shows the same issue) for compliance. The library I use parses
the entire DNS message (and fails) before I can read the rcode so
Unbound's current reply does not help me.