Setting Required for an Image does not work

Steps to reproduce

• Configure a content type based on Image

• Set field "File" on required

• Add a new content type, but don't upload the file

• Result: item is added, expected: validation error

Test scenarios

• Follow the "steps to reproduce", content item should not be added

• Edit an existing image: this should be allowed

• Edit an existing image: "Remove" checkbox should not be visible