Two bugfixes to authority-discovery

[tomaka]

Two bugfixes:

• When addresses is empty, we shouldn't just return at the beginning, as we need to erase the previous addresses. insert is really insert_or_replace, similar to what HashMap::insert does. Inserting Vec::new() should remove the previous value.

• When an authority says it has a certain PeerId, we remove that PeerId from any previous authority. If this previous authority had multiple addresses (with the same PeerId) we will call self.peer_id_to_authority_id.remove(&peer_id) multiple times with the same value in peer_id. This is fine, but the debug assert just below (debug_assert!(_old_auth.is_some());) is wrong, as it will fail the second time.

Fix paritytech/polkadot#2998

[ordian]

The debug assertion removal is fine. But I'm not sure about empty addresses. In practice inserting empty addresses should never happen

substrate/client/authority-discovery/src/worker.rs

Lines 566 to 567 in d47d162

	if !remote_addresses.is_empty() {
	self.addr_cache.insert(authority_id, remote_addresses);