Fix panic invalid memory address or nil pointer dereference in privacysettings.go

[ruskotwo]

I encountered a panic

{"level":"error","message":"Failed to fetch privacy settings when handling change: [websocket disconnected before info query returned response]","time":"2024-04-29T14:07:33Z","wacId":"01fff71b-7938-4627-bf93-102ee3794b41"}
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x48 pc=0x9911fe]

goroutine 1685089 [running]:
go.mau.fi/whatsmeow.(*Client).parsePrivacySettings(0xc067f12000?, 0xc05f86ff88, 0x0)
	go.mau.fi/[email protected]/privacysettings.go:140 +0x3be
go.mau.fi/whatsmeow.(*Client).handlePrivacySettingsNotification(0xc067f12000, 0xc0bd0d1f10?)
	go.mau.fi/[email protected]/privacysettings.go:159 +0xfa
go.mau.fi/whatsmeow.(*Client).handleAccountSyncNotification(0xc067f12000, 0xc02a112090)
	go.mau.fi/[email protected]/notification.go:199 +0x395
created by go.mau.fi/whatsmeow.(*Client).handleNotification
	go.mau.fi/[email protected]/notification.go:361 +0x69d

We got nil and error from cli.TryFetchPrivacySettings(). Error is logged, but then we go to cli.parsePrivacySettings() and pass the arguments *waBinary.Node and (!!!) nil.

This will result in an panic in most cases.

[tulir]

Thanks!