#### What type of PR is this?

/kind improvement

#### What this PR does / why we need it:

See https://github.com/halo-sigs/plugin-s3/issues/56 for more.

This PR skips permalink resolution while the object key is missing. So that the default handler will resolve permalink from annotation `storage.halo.run/external-link`

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-sigs/plugin-s3/issues/56

#### Does this PR introduce a user-facing change?

```release-note
解决导入 Halo 1.x 附件后出现“Cannot obtain object key from attachment attachment-xyz”的问题
```