[exim] multiple spam engines / reset $spam_score

hi,

i've setup my mail system to use multiple spam engines (spamassassin and
rspamd), similar to what was described in
https://lists.exim.org/lurker/message/20170620.144216.2289dbff.en.html

it works well, but if the second spam engine fails, i cannot detect
that, because the variables like $spam_score were already set
successfully in the previous scan.
the impact is, that the headers added now contain the first spam report
data.

is there any way to detect, if the second spam engine failed?
or is it possible to reset/unset the spam variables before the second run?

cheers
pille