Allow extracting elements holding transcriptions without entities

Closes #254 (closed)

dan/datasets/extract/arkindex.py

@@ -116,6 +116,9 @@ class ArkindexExtractor:
             supported_types=list(self.tokens),
         )
 
+        if not entities.count():
+            return transcription.text.strip()
+
         return self.translate(
             entities_to_xml(
                 transcription.text, entities, entity_separators=self.entity_separators