`extends`ing templates in same directory doesn't replace blocks

This file configuration was not replacing my blocks with content when extending templates:

```
theme/name/layout/page.pug extends layout with some block content
theme/name/layout/layout.pup
```
page.pug blocks don't appear in the output.

Workaround:
```
theme/name/layout/page.pug extends _partials/layout
theme/name/layout/_partials/layout.pug
```

Files in the same directory worked when using `pug-cli` to compile. Not sure why it didn't in the hexo-renderer.

Start by comparing how hexo-renderer handles the page.pug and layout.pug paths with pug-cli, using the same-directory example and the _partials/layout workaround as reproductions. Trace template resolution and verify that blocks from page.pug appear in the rendered output while the workaround continues to work.

Written by the indexing model from the issue text.