fix bug about reload knowledgebase configuration reloading (#210)

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

Issue link:#[[Link the issue
here](https://github.com/infiniflow/ragflow/issues/209)]

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/nlp/query.py

@@ -73,7 +73,7 @@ class EsQueryer:
             return True
 
         qs, keywords = [], []
-        for tt in self.tw.split(txt):  # .split(" "):
+        for tt in self.tw.split(txt)[:256]:  # .split(" "):
             if not tt:
                 continue
             twts = self.tw.weights([tt])