fix ppt file from filemanager error (#2470)

### What problem does this PR solve?

#2467

### Type of change

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

api/apps/file2document_app.py

@@ -85,6 +85,7 @@ def convert():
                         "location": file.location,
                         "size": file.size
                     })
+                    FileService.set_constant_parser(doc, file.name)
                     file2document = File2DocumentService.insert({
                         "id": get_uuid(),
                         "file_id": id,