htlcswitch: ensure we don't dispatch local HTLC's to link that aren't eligible to forward

This commit fixes an existing bug wherein we would incorrectly attempt
to forward and HTLC to a link that wasn’t yet eligible for forwarding.
This would occur when we’ve added a link to the switch, but haven’t yet
received a FundingLocked message for the channel. As a result, the
channel won’t have the next revocation point available. A logic error
prior to this commit would skip tallying the largest bandwidth rather
than skipping examining the link all together.

Fixes #464.

htlcswitch/switch.go

@@ -365,9 +365,14 @@ func (s *Switch) handleLocalDispatch(payment *pendingPayment, packet *htlcPacket
 			largestBandwidth lnwire.MilliSatoshi
 		)
 		for _, link := range links {
+			// We'll skip any links that aren't yet eligible for
+			// forwarding.
+			if !link.EligibleToForward() {
+				continue
+			}
+
 			bandwidth := link.Bandwidth()
-			if link.EligibleToForward() &&
+			if bandwidth > largestBandwidth {
-				bandwidth > largestBandwidth {
 
 				largestBandwidth = bandwidth
 			}
@@ -490,8 +495,13 @@ func (s *Switch) handlePacketForward(packet *htlcPacket) error {
 		// bandwidth.
 		var destination ChannelLink
 		for _, link := range interfaceLinks {
-			if link.EligibleToForward() &&
+			// We'll skip any links that aren't yet eligible for
-				link.Bandwidth() >= htlc.Amount {
+			// forwarding.
+			if !link.EligibleToForward() {
+				continue
+			}
+
+			if link.Bandwidth() >= htlc.Amount {
 
 				destination = link
 				break