not showing in main cat if showed in sub cat

[Shadowsong27]

This PR addresses the duplicated display in category page.

If configured to hierarchical categories, post will be present in both the main category and the sub-category.

This if statement ensures a post will only show in main category list if it does not have any sub category declared.

[kakawait]

Is not really a bug, is just the behavior from original/upstream theme (https://louisbarranqueiro.github.io/hexo-theme-tranquilpeak/all-categories/)

But we could add param to toggle the behavior.

[Shadowsong27]

@kakawait

True, hence the branch feature/*. Makes more sense to hide them from my perspective.

Thanks.