fix closing of nodes iter channel

cache/nodes.go

@@ -89,7 +89,7 @@ func (p *NodesCache) Iter() chan *element.Node {
 		// we need to Close the iter before closing the
 		// chan (and thus signaling that we are done)
 		// to avoid race where db is closed before the iterator
-		close(nodes)
+		defer close(nodes)
 		defer it.Close()
 		it.SeekToFirst()
 		for ; it.Valid(); it.Next() {