Fix/filter empty segment (#1004)

Co-authored-by: jyong <jyong@dify.ai>

api/services/dataset_service.py

@@ -891,6 +891,10 @@ class SegmentService:
         if document.doc_form == 'qa_model':
             if 'answer' not in args or not args['answer']:
                 raise ValueError("Answer is required")
+            if not args['answer'].strip():
+                raise ValueError("Answer is empty")
+        if 'content' not in args or not args['content'] or not args['content'].strip():
+            raise ValueError("Content is empty")
 
     @classmethod
     def create_segment(cls, args: dict, document: Document, dataset: Dataset):