refine redis connection (#599)

### What problem does this PR solve?

#591 

### Type of change

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

rag/app/table.py

@@ -47,6 +47,7 @@ class Excel(ExcelParser):
                 cell.value for i,
                 cell in enumerate(
                     rows[0]) if i not in missed]
+            if not headers:continue
             data = []
             for i, r in enumerate(rows[1:]):
                 rn += 1