[Facebook Page Plugin] Facebook Pages without a username do not display

### Quick summary

While working on this ticket 5632494-zd-woothemes, I found that Facebook pages without a username set do not display in the Facebook Page Plugin widget.

**Facebook page URL without username**

**Front-end**

**Facebook page URL with username**

**Front-end**

### Steps to reproduce

1. Create a new Facebook page/use an existing one without a username.
2. Add the **Facebook Page Plugin** widget to your site.
3. Copy the **Facebook Page URL** and paste it into the widget.
4. The widget will not display Facebook page content.

### What you expected to happen

For the Facebook page content to display.

### What actually happened

The Facebook page content did not display.

### Context

While working on 5632494-zd-woothemes

### Platform (Simple, Atomic, or both?)

Simple

### Theme-specific issue?

Classic themes

### Browser, operating system and other notes

_No response_

### Reproducibility

Consistent

### Severity

Some (< 50%)

### Available workarounds?

Yes, easy to implement

### Workaround details

Set a username for the Facebook page by following the steps here: https://www.facebook.com/help/121237621291199

Start by reproducing the Facebook Page Plugin widget with a Facebook page URL that has no username, then trace how the widget handles that URL. Done means the page content displays for URLs both with and without usernames; use the documented workaround as a comparison case.

Written by the indexing model from the issue text.