fix bug with empty kb (#263)

* fix bug with empty kb

* Update llm-service/app/services/query/querier.py

Co-authored-by: Copilot <[email protected]>

* small tweak

---------

Co-authored-by: Copilot <[email protected]>

Author: ewilliams-cloudera

llm-service/app/services/query/querier.py

@@ -283,6 +283,10 @@ def build_retriever(
         if data_source_id is None:
             continue
 
+        chunks = VectorStoreFactory.for_chunks(data_source_id)
+        if not chunks or not chunks.size():
+            continue
+
         embedding_model, vector_store = build_datasource_query_components(
             data_source_id
         )