amp-inline-gallery throws an error if used within an amp-list

## What's the issue?
When trying to use `amp-inline-gallery` and `amp-base-carousel` within an `amp-list` template, an error is thrown for `getImpl is not a function`. This invalidates amp and doesn't render the thumbs, however it does still render the main carousel.

I'm raising this as an issue as our current solution uses `amp-carousel` within an `amp-list` without invalidating or any other issues. I was trying to update our current solution as it uses a separate amp-list for the thumbs.

This is my first issue report with AMP so please let me know if I need to do anything further or if you need a better explanation. Thanks.


## How do we reproduce the issue?
I've replicated a basic test case with vastly reduced data that will produce the error: https://codepen.io/RickRX/pen/YzyEdvw

## What browsers are affected?
All.

## Which AMP version is affected?
2004240001480