Reverted folder.py back to using complete path to file for make_dataset and...

Reverted folder.py back to using complete path to file for make_dataset and is_valid_file rather than just the filename (#4885)
Co-authored-by: Alexander Unnervik <alex.unnervik@idiap.ch>

torchvision/datasets/folder.py

@@ -86,8 +86,8 @@ def make_dataset(
             continue
         for root, _, fnames in sorted(os.walk(target_dir, followlinks=True)):
             for fname in sorted(fnames):
-                if is_valid_file(fname):
-                    path = os.path.join(root, fname)
+                path = os.path.join(root, fname)
+                if is_valid_file(path):
                     item = path, class_index
                     instances.append(item)