FIX: Stop double prepending of window.location.origin on media URLs (PR #10275)

This fixes an issue where sometimes when composing a post and uploading a video/audio file, _loadCachedShortUrls/the uploads controller would return a full URL with origin, instead of just the URL with the host e.g. http://localhost:3000/some/video.mp4 instead of just //localhost:3000/some/video.mp4. We were prepending window.location.origin onto the URL no matter what, and since http://localhost:3000/some/video.mp4 does not match the host URL regex, we were ending up with something like http://localhost:3000http://localhost:3000/some/video.mp4 which broke composer previews. This was only noticed with a video upload in a secure upload environment.

GitHub

The title of this pull request changed from “FIX: Stop double appending of window.location.origin on media URLs” to "FIX: Stop double prepending of window.location.origin on media URLs