peer: check LocalUnrevokedCommitPoint for nil-ness as it's optional

In this commit, we modify the logWireMessage function to ensure that we
don't attempt to nil out the LocalUnrevokedCommitPoint.Curve field
unless it's actually set. We need to do this as the field as actually
optional, and we may be reading a message from a node that doesn't
support the option.

Fixes #461.

peer.go

@@ -927,7 +927,9 @@ func (p *peer) logWireMessage(msg lnwire.Message, read bool) {
 
 	switch m := msg.(type) {
 	case *lnwire.ChannelReestablish:
-		m.LocalUnrevokedCommitPoint.Curve = nil
+		if m.LocalUnrevokedCommitPoint != nil {
+			m.LocalUnrevokedCommitPoint.Curve = nil
+		}
 	case *lnwire.RevokeAndAck:
 		m.NextRevocationKey.Curve = nil
 	case *lnwire.NodeAnnouncement: