`dump-repo` command is somewhat dangerous: removing the data directory if failed.

[wxiaoguang]

DumpRepository -> migrateRepository -> uploader.Rollback -> os.RemoveAll(g.baseDir)

If migrateRepository returns error, then the data directory is removed completely.

I have run gitea dump-repo in the gitea directory, then the Gitea's data directory (including sqlite database, repositories) is removed, all lost (luckily not on production).

[a1012112796]

looks it's beter make sure the repo_dir is empty or not exist before dump-repo