ensure result adjacencies start empty

Any existing list would be mutated by result(), which is bad.

Note that all the existing newJoinResults() call sites pass in nodes
with no adjacencies, so this is purely a safety measure.

render/render.go

@@ -169,6 +169,7 @@ type joinResults struct {
 func newJoinResults(inputNodes report.Nodes) joinResults {
 	nodes := make(report.Nodes, len(inputNodes))
 	for id, n := range inputNodes {
+		n.Adjacency = nil // result() assumes all nodes start with no adjacencies
 		nodes[id] = n
 	}
 	return joinResults{nodes: nodes, mapped: map[string]string{}}
@@ -206,7 +207,7 @@ func (ret *joinResults) addChildAndChildren(m report.Node, id string, create fun
 
 // Add a copy of n straight into the results
 func (ret *joinResults) passThrough(n report.Node) {
-	n.Adjacency = nil // result() assumes all nodes start with blank lists
+	n.Adjacency = nil // result() assumes all nodes start with no adjacencies
 	ret.nodes[n.ID] = n
 	ret.mapped[n.ID] = n.ID
 }