Widget Visibility: Widget preview broken on WPCOM when visiblity settings are enabled for legacy widgets

### Impacted plugin

Jetpack

### Steps to Reproduce

Environment: On a WP.com simple site with a widget-area enabled theme (i.e "Twenty Fourteen")
1. Go to Appearance->Widgets
2. In one of the widget areas, add a "Legacy Widget" block
3. Edit the widget visiblity settings - add any condition

### A clear and concise description of what you expected to happen.

The widget preview should be visible, even when visiblity rules are set (like it happens on a non-wpcom site)

### What actually happened

The widget preview is empty when visiblity settings are set

### Other information

https://user-images.githubusercontent.com/844866/150745013-35805a80-d076-4087-901a-60bb959b74e2.mp4

### Operating System

_No response_

### OS Version

_No response_

### Browser

Chrome/Chromium, Firefox

### Browser Version(s)

_No response_