fix bug chunking:expected string or bytes-like object (#7116)

… bytes-like object

### What problem does this PR solve?
fix bug #6990 internal server error ehile chunking:expected string or
bytes-like object
_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):

Co-authored-by: unknown <taoshi.ln@chinatelecom.cn>

rag/app/table.py

@@ -193,6 +193,9 @@ def chunk(filename, binary=None, from_page=0, to_page=10000000000,
             if n in df.columns:
                 del df[n]
         clmns = df.columns.values
+        if len(clmns) != len(set(clmns)):
+            duplicates = [col for col in clmns if list(clmns).count(col) > 1]
+            raise ValueError(f"Duplicate column names detected: {set(duplicates)}")
         txts = list(copy.deepcopy(clmns))
         py_clmns = [
             PY.get_pinyins(