Error and missing images when the exported post has Google Sheets graphical elements

It seems to choke the entire post, no content visible in the body.

@catehstn found this in real-life usage.

> When you copy a graph from Google Docs, it breaks things. You have to download images and re-upload them. This is a bugger because it's a big part of why I use the Google Docs add-on for WordPress.com. Today I was drafting a post in Calypso, but found it was doing the same thing. Like choosing "copy chart” from Google Docs

Calypso editor seems to break when pasting that graph into the post body.

Cate fixed it by copy-pasting the entire Google Docs content, versus using the Add-on to sync the content over.

I was able to replicate this; I see the following error:

No source file or test is identified. Start by reproducing the failure by copying a Google Docs chart into a post and compare add-on syncing with copying the full document; the work is done when graphical elements no longer prevent the post body from being exported and images remain available.

Written by the indexing model from the issue text.