Sites tree node not properly rendered with WebSocket handshake

Describe the bug
Recording Firefox results in a site tree with a ghost record.

To Reproduce
Steps to reproduce the behavior:

1. Click the Firefox button
2. Let Firefox open, the recording will more or less automatically capture a request to https://push.services.mozilla.com/
3. There will be a response to HTTP/1.1 101 Switching Protocols
4. The Sites view doesn't show a domain at all, just a page icon with a lock

GET https://push.services.mozilla.com/ HTTP/1.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:70.0) Gecko/20100101 Firefox/70.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Sec-WebSocket-Version: 13
Origin: wss://push.services.mozilla.com/
Sec-WebSocket-Protocol: push-notification
Sec-WebSocket-Key: jytOg54RWyXBdRlndSmcyA==
Connection: keep-alive, Upgrade
Pragma: no-cache
Cache-Control: no-cache
Upgrade: websocket
Host: push.services.mozilla.com

HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Accept: NCEMNlyLOxOx1DM+xolfzkJRieE=

Expected behavior
A normal line item in the Sites panel with a domain name

Screenshots
If applicable, add screenshots to help explain your problem.

Software versions

• ZAP: 2.8.0
• Add-on:
• OS: Windows 10
• Java:
• Browser: Firefox 70.0.1

Reproduce the Firefox recording described in the issue and inspect the Sites view entry created for the WebSocket handshake. Trace how the HTTP 101 Switching Protocols response is represented and rendered. Done means the Sites panel shows a normal line item with the push.services.mozilla.com domain instead of a ghost record.