Always add a suitable error if we fail to decode

Always add a suitable error if we fail to decode

We're always supposed to add the fallback "unsupported" error if we don't
have anything better. However in some cases this wasn't happening because
we were incorrectly setting "flag_construct_called" - even though the
construct function had failed.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21603)

(cherry picked from commit 564e5b754a4680dfad38585dd73bcf025567b448)