Correctly apply transcriptions filter

Closes #53 (closed)

atr_data_generator/extract/db.py

@@ -77,7 +77,7 @@ def get_children_info(
 
     # Filter by transcription source
     if sources:
-        transcriptions.where(parse_sources(sources.copy()))
+        transcriptions = transcriptions.where(parse_sources(sources.copy()))
 
     # Additional ordering in case there are identical names
     return transcriptions.order_by(Transcription.element.name, Transcription.element_id)