Ignore exceptions when no index ahead. (#5047)

### What problem does this PR solve?

### Type of change

- [x] Refactoring

api/apps/kb_app.py

@@ -301,7 +301,7 @@ def knowledge_graph(kb_id):
     }
 
     obj = {"graph": {}, "mind_map": {}}
-    if not settings.docStoreConn.indexExist(search.index_name(kb.tenant_id)):
+    if not settings.docStoreConn.indexExist(search.index_name(kb.tenant_id), kb_id):
         return get_json_result(data=obj)
     sres = settings.retrievaler.search(req, search.index_name(kb.tenant_id), [kb_id])
     if not len(sres.ids):

rag/nlp/search.py

@@ -449,6 +449,8 @@ class Dealer:
         return res
 
     def all_tags(self, tenant_id: str, kb_ids: list[str], S=1000):
+        if not self.docStoreConn.indexExist(index_name(tenant_id), kb_ids[0]):
+            return []
         res = self.dataStore.search([], [], {}, [], OrderByExpr(), 0, 0, index_name(tenant_id), kb_ids, ["tag_kwd"])
         return self.dataStore.getAggregation(res, "tag_kwd")