params: handle the modified sentinel.

The param builder and the params from text helpers also need to be modified
aware.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/11601)

crypto/param_build.c

@@ -312,7 +312,7 @@ static OSSL_PARAM *param_bld_convert(OSSL_PARAM_BLD *bld, OSSL_PARAM *param,
         param[i].key = pd->key;
         param[i].data_type = pd->type;
         param[i].data_size = pd->size;
-        param[i].return_size = 0;
+        param[i].return_size = OSSL_PARAM_UNMODIFIED;
 
         if (pd->secure) {
             p = secure;

crypto/params_from_text.c

@@ -157,7 +157,7 @@ static int construct_from_text(OSSL_PARAM *to, const OSSL_PARAM *paramdef,
     *to = *paramdef;
     to->data = buf;
     to->data_size = buf_n;
-    to->return_size = 0;
+    to->return_size = OSSL_PARAM_UNMODIFIED;
 
     return 1;
 }