routing: populate the chain filter before calling syncGraphWithChain

In this commit we fix an existing bug within the ChannelRouter. Before
this commit, we would sync our graph prune state, *then* update the
cain filter. This is incorrect as the blocks we manually pruned may
have included channel closing transactions. As a result, we would miss
the pruning of a set of channels, and assume that they were still
active.

In this commit, we fix this by reversing the order: we first update the
chain filter and THEN sync the channel graph.

routing/router.go

@@ -273,14 +273,10 @@ func (r *ChannelRouter) Start() error {
 	r.newBlocks = r.cfg.ChainView.FilteredBlocks()
 	r.staleBlocks = r.cfg.ChainView.DisconnectedBlocks()
 
-	// Before we begin normal operation of the router, we first need to
+	// Before we perform our manual block pruning, we'll construct and
-	// synchronize the channel graph to the latest state of the UTXO set.
-	if err := r.syncGraphWithChain(); err != nil {
-		return err
-	}
-
-	// Once we've concluded our manual block pruning, we'll constrcut and
 	// apply a fresh chain filter to the active FilteredChainView instance.
+	// We do this before, as otherwise we may miss on-chain events as the
+	// filter hasn't properly been applied.
 	channelView, err := r.cfg.Graph.ChannelView()
 	if err != nil && err != channeldb.ErrGraphNoEdgesFound {
 		return err
@@ -291,6 +287,12 @@ func (r *ChannelRouter) Start() error {
 		return err
 	}
 
+	// Before we begin normal operation of the router, we first need to
+	// synchronize the channel graph to the latest state of the UTXO set.
+	if err := r.syncGraphWithChain(); err != nil {
+		return err
+	}
+
 	r.wg.Add(1)
 	go r.networkHandler()
 
@@ -371,7 +373,7 @@ func (r *ChannelRouter) syncGraphWithChain() error {
 		log.Infof("channel graph is stale. Disconnecting block %v "+
 			"(hash=%v)", pruneHeight, pruneHash)
 		// Prune the graph for every channel that was opened at height
-		// >= pruneHeigth.
+		// >= pruneHeight.
 		_, err := r.cfg.Graph.DisconnectBlockAtHeight(pruneHeight)
 		if err != nil {
 			return err
@@ -431,7 +433,8 @@ func (r *ChannelRouter) syncGraphWithChain() error {
 		// With the spent outputs gathered, attempt to prune the
 		// channel graph, also passing in the hash+height of the block
 		// being pruned so the prune tip can be updated.
-		closedChans, err := r.cfg.Graph.PruneGraph(spentOutputs, nextHash,
+		closedChans, err := r.cfg.Graph.PruneGraph(spentOutputs,
+			nextHash,
 			nextHeight)
 		if err != nil {
 			return err