[data.classify.nih_cxr14] Fix file access

src/mednet/data/classify/nih_cxr14.py

@@ -222,7 +222,7 @@ class RawDataLoader(BaseDataLoader):
 
         # N.B.: some NIH CXR-14 images are encoded as color PNGs with an alpha
         # channel.  Most, are grayscale PNGs
-        image = PIL.Image.open(self.datadir / sample[0]).convert(mode="L")
+        image = PIL.Image.open(self.datadir / file_path).convert(mode="L")
         image = to_dtype(to_image(image), torch.float32, scale=True)
         image = tv_tensors.Image(image)