Add more checks for canceled contexts

internal/walker/rewriter.go

@@ -116,6 +116,10 @@ func (t *TreeRewriter) RewriteTree(ctx context.Context, repo BlobLoadSaver, node
 
 	tb := restic.NewTreeJSONBuilder()
 	for _, node := range curTree.Nodes {
+		if ctx.Err() != nil {
+			return restic.ID{}, ctx.Err()
+		}
+
 		path := path.Join(nodepath, node.Name)
 		node = t.opts.RewriteNode(node, path)
 		if node == nil {

internal/walker/walker.go

@@ -57,6 +57,10 @@ func walk(ctx context.Context, repo restic.BlobLoader, prefix string, parentTree
 	})
 
 	for _, node := range tree.Nodes {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+
 		p := path.Join(prefix, node.Name)
 
 		if node.Type == "" {