localchans: recreate missing edge if not found

If a node contains a channel, but doesn't have a corresponding edge in
the graph database, updating the channel policy would fail. In this
commit the edge is recreated if the channel exists. This ensures a node
can recover from a missing edge in the graph database by calling
updatechanpolicy.

server.go

@@ -1112,10 +1112,15 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 
 	//nolint:lll
 	s.localChanMgr = &localchans.Manager{
+		SelfPub:                   nodeKeyDesc.PubKey,
+		DefaultRoutingPolicy:      cc.RoutingPolicy,
 		ForAllOutgoingChannels:    s.graphBuilder.ForAllOutgoingChannels,
 		PropagateChanPolicyUpdate: s.authGossiper.PropagateChanPolicyUpdate,
 		UpdateForwardingPolicies:  s.htlcSwitch.UpdateForwardingPolicies,
 		FetchChannel:              s.chanStateDB.FetchChannel,
+		AddEdge: func(edge *models.ChannelEdgeInfo) error {
+			return s.graphBuilder.AddEdge(edge)
+		},
 	}
 
 	utxnStore, err := contractcourt.NewNurseryStore(