Move manual dir check to the top of the _split_generators method

The idea is that the manual download instructions would be displayed instead of the generic DatasetViewer is disabled message

tacred.py

@@ -313,12 +313,6 @@ class Tacred(datasets.GeneratorBasedBuilder):
         # dl_manager is a datasets.download.DownloadManager that can be used to download and extract URLs
         # It can accept any type or nested list/dict and will give back the same structure with the url replaced with path to local files.
         # By default the archives will be extracted and a path to a cached folder where they are extracted is returned instead of the archive
-        patch_files = {}
-        if self.config.name == "revisited":
-            patch_files = dl_manager.download_and_extract(_PATCH_URLs)
-        elif self.config.name == "re-tacred":
-            patch_files = dl_manager.download_and_extract(_RETACRED_PATCH_URLs)
-
         data_dir = os.path.abspath(os.path.expanduser(dl_manager.manual_dir))
 
         if not os.path.exists(data_dir):
@@ -328,6 +322,12 @@ class Tacred(datasets.GeneratorBasedBuilder):
                 )
             )
 
+        patch_files = {}
+        if self.config.name == "revisited":
+            patch_files = dl_manager.download_and_extract(_PATCH_URLs)
+        elif self.config.name == "re-tacred":
+            patch_files = dl_manager.download_and_extract(_RETACRED_PATCH_URLs)
+
         return [
             datasets.SplitGenerator(
                 name=datasets.Split.TRAIN,