Refa: add result to callback for agent tool use. (#9137)

### What problem does this PR solve?


### Type of change

- [x] Refactoring

deepdoc/parser/html_parser.py

@@ -29,7 +29,6 @@ def get_encoding(file):
 
 class RAGFlowHtmlParser:
     def __call__(self, fnm, binary=None):
-        txt = ""
         if binary:
             encoding = find_codec(binary)
             txt = binary.decode(encoding, errors="ignore")