don't add digest alias if signature algorithm is undefined

crypto/evp/names.c

@@ -86,7 +86,7 @@ int EVP_add_digest(const EVP_MD *md)
 	r=OBJ_NAME_add(OBJ_nid2ln(md->type),OBJ_NAME_TYPE_MD_METH,(const char *)md);
 	if (r == 0) return(0);
 
-	if (md->type != md->pkey_type)
+	if (md->pkey_type && md->type != md->pkey_type)
 		{
 		r=OBJ_NAME_add(OBJ_nid2sn(md->pkey_type),
 			OBJ_NAME_TYPE_MD_METH|OBJ_NAME_ALIAS,name);