routing: prune channels only if both edges are present

We do this to ensure we don't prune too aggressively, as it's possible
that we've only received the channel announcement for a channel, but not
its accompanying channel updates.

routing/pathfind_test.go

@@ -15,6 +15,7 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -303,6 +304,7 @@ type testChannelPolicy struct {
 	MaxHTLC     lnwire.MilliSatoshi
 	FeeBaseMsat lnwire.MilliSatoshi
 	FeeRate     lnwire.MilliSatoshi
+	LastUpdate  time.Time
 }
 
 type testChannelEnd struct {
@@ -319,6 +321,7 @@ func defaultTestChannelEnd(alias string, capacity btcutil.Amount) *testChannelEn
 			MaxHTLC:     lnwire.NewMSatFromSatoshis(capacity),
 			FeeBaseMsat: lnwire.MilliSatoshi(1000),
 			FeeRate:     lnwire.MilliSatoshi(1),
+			LastUpdate:  testTime,
 		},
 	}
 }
@@ -500,7 +503,7 @@ func createTestGraphFromChannels(testChannels []*testChannel) (*testGraphInstanc
 				MessageFlags:              msgFlags,
 				ChannelFlags:              0,
 				ChannelID:                 channelID,
-				LastUpdate:                testTime,
+				LastUpdate:                testChannel.Node1.LastUpdate,
 				TimeLockDelta:             testChannel.Node1.Expiry,
 				MinHTLC:                   testChannel.Node1.MinHTLC,
 				MaxHTLC:                   testChannel.Node1.MaxHTLC,
@@ -522,7 +525,7 @@ func createTestGraphFromChannels(testChannels []*testChannel) (*testGraphInstanc
 				MessageFlags:              msgFlags,
 				ChannelFlags:              lnwire.ChanUpdateDirection,
 				ChannelID:                 channelID,
-				LastUpdate:                testTime,
+				LastUpdate:                testChannel.Node2.LastUpdate,
 				TimeLockDelta:             testChannel.Node2.Expiry,
 				MinHTLC:                   testChannel.Node2.MinHTLC,
 				MaxHTLC:                   testChannel.Node2.MaxHTLC,