Correctly resolve trust_remote_code=None for AutoTokenizer (#28419)

* Correctly resolve trust_remote_code=None for AutoTokenizer

* Second attempt at a proper resolution

src/transformers/models/auto/tokenization_auto.py

@@ -770,7 +770,13 @@ class AutoTokenizer:
                 tokenizer_auto_map = config.auto_map["AutoTokenizer"]
 
         has_remote_code = tokenizer_auto_map is not None
-        has_local_code = config_tokenizer_class is not None or type(config) in TOKENIZER_MAPPING
+        has_local_code = type(config) in TOKENIZER_MAPPING or (
+            config_tokenizer_class is not None
+            and (
+                tokenizer_class_from_name(config_tokenizer_class) is not None
+                or tokenizer_class_from_name(config_tokenizer_class + "Fast") is not None
+            )
+        )
         trust_remote_code = resolve_trust_remote_code(
             trust_remote_code, pretrained_model_name_or_path, has_local_code, has_remote_code
         )