fix sequence2txt error and usage total token issue (#2961)

### What problem does this PR solve?

#1363

### Type of change

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

api/utils/file_utils.py

@@ -197,6 +197,7 @@ def thumbnail_img(filename, blob):
             pass
     return None
 
+
 def thumbnail(filename, blob):
     img = thumbnail_img(filename, blob)
     if img is not None:
@@ -205,6 +206,7 @@ def thumbnail(filename, blob):
     else:
         return ''
 
+
 def traversal_files(base):
     for root, ds, fs in os.walk(base):
         for f in fs: