Completions that depends on Antigen being fully loaded fail

- `antigen-theme`
- `antigen-update`, `antigen-purge`

It failed to fully load antigen when required. See [here](https://github.com/zsh-users/antigen/blob/develop/src/_antigen#L68).

Caused by antigen wrapper and [this](https://github.com/zsh-users/antigen/blob/develop/src/ext/cache.zsh#L41) check.