chainntnfs: patch debug logs and fix StartHeight

Make sure we patch the `StartHeight` for btcd notifier.

chainntnfs/bitcoindnotify/bitcoind.go

@@ -833,8 +833,12 @@ func (b *BitcoindNotifier) RegisterSpendNtfn(outpoint *wire.OutPoint,
 			return nil, err
 		}
 
-		if uint32(blockHeight) > ntfn.HistoricalDispatch.StartHeight {
-			ntfn.HistoricalDispatch.StartHeight = uint32(blockHeight)
+		spentHeight := uint32(blockHeight)
+		chainntnfs.Log.Debugf("Outpoint(%v) has spent at height %v",
+			outpoint, spentHeight)
+
+		if spentHeight > ntfn.HistoricalDispatch.StartHeight {
+			ntfn.HistoricalDispatch.StartHeight = spentHeight
 		}
 	}