🐛 Bug: nil pointer dereference when using `RemoteAddr` on disconnect handler

[si3nloong]

📜 Description

I have a log service to track the connection offline and we need to retrieve the IP from remote addr, but it return nil because the connection had closed, the connection will be always nil, so this will result in invalid memory address or nil pointer dereference

I have a PR to fix this specific issue.

👟 Reproduction steps

1. Charger disconnect from the central system
2. Trigger disconnect handler
3. Use RemoteAddr, it throw invalid memory address or nil pointer dereference

👍 Expected behavior

The server shouldn't panic

👎 Actual Behavior

The server throw `invalid memory address or nil pointer dereference` and panic

What OCPP version are you using?

• OCPP 1.6
• OCPP 2.0.1

Are you using any OCPP extensions?

• OCPP 1.6 Security
• OCPP 1.6 Plug and Charge

release version

v0.19.1-0.20250817142028-b22429c28ebb

📃 Provide any additional context for the Bug.

No response

👀 Have you spent some time to check if this bug has been found before?

• I checked and didn't find a similar issue

[AndrewYEEE]

maybe you can add a nil check for RemoteAddr() on ws/websocke.go

 // Returns the address of the remote peer.
func (websocket *WebSocket) RemoteAddr() net.Addr {
        if websocket.connection == nil {
                return nil
        }
	return websocket.connection.RemoteAddr()
}