Raise an assertion error if no training images have been found.

modules/textual_inversion/dataset.py

@@ -82,6 +82,7 @@ class PersonalizedBase(Dataset):
 
             self.dataset.append(entry)
         
+        assert len(self.dataset) > 1, "No images have been found in the dataset."
         self.length = len(self.dataset) * repeats
 
         self.initial_indexes = np.arange(self.length) % len(self.dataset)