[Sprint/UnderstoodUnicorn](fix): Fixed inability to cancel uploaded image. #2334

Summary

Closes #2334 (closed)

This merge request addresses an issue on production right now where cancelling an image upload causes everything to break.

Steps to test

1. Fully upload an image
2. Cancel it
3. It should cancel
4. Upload a new image

Repeat but stop the image mid upload.

All should work fine.

Estimated Regression Scope

This change should affect media uploads across the site. Comments, feeds etc. There is an issue where-in you can get the poster to show no attachment after hitting upload - this occurs when it is waiting for the previous XHR to resolve.

Issues handled in another MR

In group chats, when you cancel, an outline window appears #2349 (closed)