When multiple peers had multiplayer authority over a MultiplayerSpawner
and spawned nodes that used a MultiplayerSynchronizer that were later
deleted, these peers would stop syncing random nodes from other peers
because the net_id of said spawned nodes was not unique over all peers.
The net_id was the only criteria that was looked at to stop syncing the
node.
This commit fixes this by also looking at the peer the node came from.
Sander Vanhove
73c95baa52