Fix potential memory leak in dh_ameth.c

Free dukm in error handling of dh_cms_encrypt()

Fixes #10294
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NPatrick Steuer <patrick.steuer@de.ibm.com>
(Merged from https://github.com/openssl/openssl/pull/10310)

crypto/dh/dh_ameth.c

@@ -976,6 +976,7 @@ static int dh_cms_encrypt(CMS_RecipientInfo *ri)
  err:
     OPENSSL_free(penc);
     X509_ALGOR_free(wrap_alg);
+    OPENSSL_free(dukm);
     return rv;
 }