Don't crash if an unrecognised digest is used with dsa_paramgen_md
Don't crash if an unrecognised digest is used with dsa_paramgen_md

Reviewed-by: Rich Salz <c04971a99e5a9ee80eaab4b1deb37e845b0bd697@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5800)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl