Image Uploader Fails If Asset Without Thumbnail Recently Uploaded

[Jefferson Rabb]

Describe the bug
If an asset without a thumbnail (e.g. a PDF) is among the media items displayed when Insert Image is clicked, the Liveblog interface breaks and can only be restored by reloading the page.

Originally reported on https://in-gl.de/2020/03/23/liveblog-corona-in-gl-23-3/.

To Reproduce
Steps to reproduce the behavior:

1. Navigate to Media Library and upload a PDF.
2. View published Liveblog page.
3. Click Insert Image.
4. Observe Liveblog breakage, console log error similar to screenshot below.

Screenshots
Video:
https://cloudup.com/cLIynAS0wQv

Console log:

Expected behavior
Image upload works normally.