BUG: Background image preview not displayed in the editor widget

### GrapesJS version

- [x] I confirm to use the latest version of GrapesJS

### GrapesJS MJML version

- [x] I confirm to use the latest version of GrapesJS MJML

### What browser are you using?

Any

### Reproducible demo link

https://grapesjs.com/demo-mjml.html

### Describe the bug

**How to reproduce the bug?**
1. Drag Hero widget somewhere on the page
2. Select it and go to style manager, decorations - the "Background url" widget will allow to remove or change it but will not show any preview of the image (the preview DIV remains empty).

This also happens on any other element allowing a background image.

**What is the expected behavior?**
Image preview visible

**What is the current behavior?**
Image preview missing

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct