Reset loading back to true

This is so that when going from

- https://gerrit-review.googlesource.com/admin/repos/Public-Projects,access

to

- https://gerrit-review.googlesource.com/admin/repos/All-Projects,access

will show loading as it needs to be reset.

Bug: Issue 9861
Change-Id: I10e75e1592d73e140005d6ae5a573e5e2b1dbbb5

polygerrit-ui/app/elements/admin/gr-repo-access/gr-repo-access.js

@@ -133,6 +133,8 @@
      * @return {!Promise}
      */
     _repoChanged(repo) {
+      this._loading = true;
+
       if (!repo) { return Promise.resolve(); }
 
       return this._reload(repo);