Fix:local_es_tag (#7534)

Two Case when local  Es tag search has result which is filtered by score
1: Doc has empty tag,and not visi LLM
2: Code may use empty examples in Prompt for LLM search tag

Co-authored-by: huangfuqunze <huangfuqunze.hfqz@alibaba-inc.com>

rag/svr/task_executor.py

 
         docs_to_tag = []
         for d in docs:
-            if settings.retrievaler.tag_content(tenant_id, kb_ids, d, all_tags, topn_tags=topn_tags, S=S):
+            if settings.retrievaler.tag_content(tenant_id, kb_ids, d, all_tags, topn_tags=topn_tags, S=S) and len(d[TAG_FLD]) > 0:
                 examples.append({"content": d["content_with_weight"], TAG_FLD: d[TAG_FLD]})
             else:
                 docs_to_tag.append(d)