UiWebsocket.py: "'SiteStorage' object has no attribute 'piecefields'"

### Step 1: Please describe your environment

* ZeroNet version: ZeroNet-py3 0.7.2 (rev 4553)
* Operating system: Debian Buster
* Web browser: Google Chrome
* Tor status: always
* Opened port: no
* Special configuration: UiPassword is on, access through local network.

### Step 2: Describe the problem:

#### Steps to reproduce:

1. Open link http://:43110/149EPBN4hQRpwj5TcoPETepnoXHCUXzaCN/ (YouTube on ZeroNet)
2. It suddenly appears a message "Internal error: AttributeError("'SiteStorage' object has no attribute 'piecefields'"): 'SiteStorage' object has no attribute 'piecefields' >> UiWebsocket.py line 80 > 236 > OptionalManager/UiWebsocketPlugin.py line 169 > 67" on top right corner, and the zite does not show the video list.

#### Observed Results:


#### Expected Results:

Being able to use YouTube on ZeroNet again.