close a nexus' vdps when at the last child

we want to delay destruction until we have delivered all of the
worklist, but we need to fini the vdps in the same order as
varnish-cache serial esi.

the error case is gzgz which needs to update the parent at the right
point in time

src/vdp_pesi.c

@@ -1813,6 +1813,16 @@ bytes_push_worklist(struct req *req, struct bytes_tree *tree,
 
 		if (retval)
 			break;
+
+		if (VSTAILQ_NEXT(node, sibling) == NULL) {
+			parent = node->parent;
+			if (parent->parent == NULL)
+				(void) 0;
+			else if (parent->state < ST_CLOSED)
+				assert(next == NULL);
+			else
+				VDP_close(parent->nexus.req);
+		}
 		node = next;
 	}