Avoid crashing if tensorflow is not installed for VTAB (#131)

Author: bryant1410

clip_benchmark/datasets/tfds.py

@@ -9,8 +9,11 @@ def download_tfds_dataset(name, data_dir=None):
     builder.download_and_prepare()
 
 def disable_gpus_on_tensorflow():
-    import tensorflow as tf
-    tf.config.set_visible_devices([], 'GPU')  
+    try:
+        import tensorflow as tf
+        tf.config.set_visible_devices([], 'GPU')  
+    except ImportError:
+        pass
 
 class VTABIterableDataset(torch.utils.data.IterableDataset):