Parsing functions are at liberty to return:

1:  when parsing on processing of the parsed value succeeded
0:  when the parsed keyword is unknown
-1: when the parsed value processing failed

Some parsing functions didn't do this quite right, they returned 0
when they should have returned -1, causing a message like this:

    Line 123: unknown keyword PeerKey

When this message (which is displayed when the parsing function
returns -1) would have been more appropriate:

    Line 123: error processing keyword PeerKey = ffdhe2048-2-pub
Reviewed-by: NTomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/9682)

(cherry picked from commit f42c225d7f9a0bce0bf46103343402d3f0ad742f)