refac(bitswap) nil slices are 'range'able

exchange/bitswap/bitswap.go

@@ -117,7 +117,6 @@ func (bs *bitswap) ReceiveMessage(
 
 	bs.strategy.MessageReceived(p, incoming)
 
-	if incoming.Blocks() != nil {
 	for _, block := range incoming.Blocks() {
 		err := bs.blockstore.Put(block) // FIXME(brian): err ignored
 		if err != nil {
@@ -129,9 +128,7 @@ func (bs *bitswap) ReceiveMessage(
 			return nil, nil, err
 		}
 	}
-	}
 
-	if incoming.Wantlist() != nil {
 	for _, key := range incoming.Wantlist() {
 		if bs.strategy.ShouldSendBlockToPeer(key, p) {
 			block, errBlockNotFound := bs.blockstore.Get(key)
@@ -144,7 +141,6 @@ func (bs *bitswap) ReceiveMessage(
 			return p, message, nil
 		}
 	}
-	}
 	return nil, nil, nil
 }