No warning shown when DnD duplicated images

Description

Steps to reproduce:
1. Create a page with a xhtmlstring property, such as product page - Alloy Plan.
2. Drag and drop an image to the xhtmlstring property.
=> The image is uploaded to "For this page" folder.
3. Drag and drop a different image with the same name as the one in step 2.

Expected:
Should show a warning message that you're about to overwrite an image.

Actual:
Image is overwritten without warning.