Folder displays http not found exception when image path cannot be loaded.

Prereq.: "Can be a thumbnail" set to true in image field. APP_ENV dev.

Steps:

1. Publish new image.
2. Find the file in public/var and change its name.
3. Reload cache.
4. In admin panel try to load the folder that contains the image.

Actual result: HTTP 404 Not Found exception is displayed.
Expected result: Missing file is handled more gently.

Remarks: Does not occur on v2.5.