No more DPI adjusting

Closes #191 (closed)

Needs testing on a real dataset because training test is failing only because optimizers are different.

dan/datasets/extract/arkindex.py

@@ -384,6 +384,9 @@ class ArkindexExtractor:
             subword_vocab_size=self.subword_vocab_size,
         )
 
+        if not tokenizer.sentencepiece_model:
+            return
+
         for level, tokenize in (
             ("characters", tokenizer.char_tokenize),
             ("words", tokenizer.word_tokenize),
@@ -478,6 +481,11 @@ class ArkindexExtractor:
                     pbar.update()
                     pbar.refresh()
 
+        if not self.data:
+            raise Exception(
+                "No data was extracted using the provided export database and parameters."
+            )
+
         self.download_images()
         self.format_lm_files()
         self.export()