fix bug about divided by zero (#1482)

### What problem does this PR solve?


### Type of change

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

deepdoc/parser/pdf_parser.py

         )
 
         # solve char content confusion
-        record_error_length, ct = 0, 1
+        record_error_length, ct = 0, 0.001
         for c in chars[0:128]:
             ii = Recognizer.find_overlapped(c, bxs)
             if ii is None: