Image Editor does not work when IO handler is set.

Prereq.: Setup with a static server for images (ref. https://doc.ezplatform.com/en/3.1/guide/file_management/#using-a-static-server-for-images)

Steps:

1. Log in to admin panel.
2. Start editing an image.
3. Open Image Editor.
4. Try to flip horizontally.

Actual result: Image is not flipped, console error occurs:

Uncaught DOMException: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.

Expected result: Image can be flipped without errors.

Remarks: Affects Crop also.