Edge Case: Changing file type from UV renderable file to non-UV renderable file keeps thumbnail of previous version

[jeremyf]

Per #2910 (comment)

I did a QA check on this and it mostly seems to be working. Editing a file with a new version generally replaced it in the viewer and the thumbnail.

There was one edgecase though: when updated with a file type that isn't renderable in the UV (a svg in this case), it displayed the expected empty "No preview available/download this file" prompt in the place of the viewer, but was still showing a thumbnail of the last version

Related to #2910

Possible things to consider:

1. The change in file type may cause thumbnail issues
2. The thumbnail issue is something unrelated (e.g. caching past versions)