Update table.py to convert clmns to string (#414)

### What problem does this PR solve?


### Type of change

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

rag/app/table.py

@@ -199,7 +199,7 @@ def chunk(filename, binary=None, from_page=0, to_page=10000000000,
                 re.sub(
                     r"(/.*|（[^（）]+?）|\([^()]+?\))",
                     "",
-                    n),
+                    str(n)),
                 '_')[0] for n in clmns]
         clmn_tys = []
         for j in range(len(clmns)):
@@ -208,7 +208,7 @@ def chunk(filename, binary=None, from_page=0, to_page=10000000000,
             df[clmns[j]] = cln
             if ty == "text":
                 txts.extend([str(c) for c in cln if c])
-        clmns_map = [(py_clmns[i].lower() + fieds_map[clmn_tys[i]], clmns[i].replace("_", " "))
+        clmns_map = [(py_clmns[i].lower() + fieds_map[clmn_tys[i]], str(clmns[i]).replace("_", " "))
                      for i in range(len(clmns))]
 
         eng = lang.lower() == "english"  # is_english(txts)