Summary:
Fix the following error while running `make crash_test`
```
Traceback (most recent call last):
  File "tools/db_crashtest.py", line 705, in <module>
    main()
  File "tools/db_crashtest.py", line 696, in main
    blackbox_crash_main(args, unknown_args)
  File "tools/db_crashtest.py", line 479, in blackbox_crash_main
    + list({'db': dbname}.items())), unknown_args)
  File "tools/db_crashtest.py", line 414, in gen_cmd
    finalzied_params = finalize_and_sanitize(params)
  File "tools/db_crashtest.py", line 331, in finalize_and_sanitize
    dest_params.get("user_timestamp_size") > 0):
TypeError: '>' not supported between instances of 'NoneType' and 'int'
```

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8091

Test Plan: make crash_test

Reviewed By: ltamasi

Differential Revision: D27268276

Pulled By: riversand963

fbshipit-source-id: ed2873b9587ecc51e24abc35ef2bd3d91fb1ed1b