Increase display size when path is also equals to it

Length and index are always shifted by 1.

issue8506
review273621002

src/view/tree.js

@@ -747,7 +747,7 @@
                 return;
             }
             path = this.record.get_index_path(this.group);
-            if (this.rows.length < path[0]) {
+            if (this.rows.length <= path[0]) {
                 this.display_size = this.group.length;
                 this.display();
             }