Fix csv reader exception. (#4628)

### What problem does this PR solve?

#4552
### Type of change

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

rag/app/qa.py

@@ -394,7 +394,7 @@ def chunk(filename, binary=None, lang="Chinese", callback=None, **kwargs):
                     f"{len(fails)} failure, line: %s..." % (",".join(fails[:3])) if fails else "")))
 
         if question:
-            res.append(beAdoc(deepcopy(doc), question, answer, eng, len(reader)))
+            res.append(beAdoc(deepcopy(doc), question, answer, eng, len(list(reader))))
 
         callback(0.6, ("Extract Q&A: {}".format(len(res)) + (
             f"{len(fails)} failure, line: %s..." % (",".join(fails[:3])) if fails else "")))