use config.data_dir instead of checking if url points to local directory

this fixes "NotImplementedError: os.path.isdir is not extended to support URLs in streaming mode" when calling with a remote (zip) target as url.

brat.py

@@ -301,20 +301,17 @@ class Brat(datasets.GeneratorBasedBuilder):
     def _split_generators(self, dl_manager):
         """Returns SplitGenerators."""
 
-        subdirectory_mapping = self.config.subdirectory_mapping
-
-        # since subclasses of BuilderConfig are not allowed to define
-        # attributes without defaults, check here
-        assert self.config.url is not None, "data url not specified"
-
-        # if url points to a local directory, just point to that
-        if path.exists(self.config.url) and path.isdir(self.config.url):
-            data_dir = self.config.url
-        # otherwise, download and extract
+        if self.config.data_dir is not None:
+            data_dir = self.config.data_dir
+            logging.warning(f"load from data_dir: {data_dir}")
         else:
+            # since subclasses of BuilderConfig are not allowed to define
+            # attributes without defaults, check here
+            assert self.config.url is not None, "data url not specified"
+
             data_dir = dl_manager.download_and_extract(self.config.url)
-        logging.info(f"load from data dir: {data_dir}")
 
+        subdirectory_mapping = self.config.subdirectory_mapping
         # if no subdirectory mapping is provided, ...
         if subdirectory_mapping is None:
             # ... use available subdirectories as split names ...