Additional assert on dataset

Author: R-N

modules/textual_inversion/dataset.py

@@ -42,6 +42,8 @@ def __init__(self, data_root, width, height, repeats, flip_p=0.5, placeholder_to
         self.lines = lines
 
         assert data_root, 'dataset directory not specified'
+        assert os.path.isdir(data_root), "Dataset directory doesn't exist"
+        assert os.listdir(data_root), "Dataset directory is empty"
 
         cond_model = shared.sd_model.cond_stage_model