discovery: use inclusive range in FilterChannelRange

FilterChannelRange takes an inclusive range, so it was possible for us
to return channels for an additional block that was not requested.

discovery/syncer.go

@@ -814,8 +814,9 @@ func (g *GossipSyncer) replyChanRangeQuery(query *lnwire.QueryChannelRange) erro
 	// Next, we'll consult the time series to obtain the set of known
 	// channel ID's that match their query.
 	startBlock := query.FirstBlockHeight
+	endBlock := startBlock + query.NumBlocks - 1
 	channelRange, err := g.cfg.channelSeries.FilterChannelRange(
-		query.ChainHash, startBlock, startBlock+query.NumBlocks,
+		query.ChainHash, startBlock, endBlock,
 	)
 	if err != nil {
 		return err