Update on "Pass one NDM to backend init"

Take external NDM if it exists, otherwise internal.

Note: by default, xnnpack uses the named_data_map. Constants are not stored with the delegated blob anymore.

Differential Revision: [D73679710](https://our.internmc.facebook.com/intern/diff/D73679710/)

[ghstack-poisoned]

Author: lucylq

runtime/executor/method.cpp

@@ -810,7 +810,7 @@ Error Method::init(
         NotSupported,
         "NamedDataMap merge not supported; both pte_data_map and named_data_map are non-empty. If you see this error please file an issue at https://github.com/pytorch/executorch/issues");
 
-    if (!named_data_map && named_data_map->get_num_keys().get() > 0) {
+    if (named_data_map && named_data_map->get_num_keys().get() > 0) {
       named_data_map = pte_data_map;
     }