RecursionError using Latest Pages block with article pages

#### Describe the bug
When using Latest Pages block on an article page, and selecting parent article landing page as source, if the current article page is in the listed latest pages, it crashes. The article landing page is also crashing.

#### Steps to reproduce
Steps to reproduce the behavior:
1. On an article page, use the Latest Pages block
2. Select parent page of current article as source
3. Select any number of pages to list, making sure the current page will be listed with the ordering specified in the parent’s LAYOUT tab.
4. RecursionError

#### Expected behavior
It should list all latest pages, including or excluding the current page.

Start by reproducing the RecursionError with the Latest Pages block on an article page, using its parent article landing page as the source and an ordering that includes the current page. Trace the Latest Pages block and page-listing entry points to identify the recursive path. Done means the block lists the requested latest pages without crashing, whether or not the current page is included.

索引モデルが issue の本文から書いたものです。