Patch to make re-overriding libraries in subthemes a not-terrible experience also fixes this

Somehow.  Kind of surprising; i would have expected it maybe to allow Claro to start overriding
libraries the 'correct' way and *then* the subtheme inheritance working, but i'm not going to
complain that this was an instant fix to https://www.drupal.org/project/drupal/issues/2856499
as well as to https://www.drupal.org/project/drupal/issues/2642122

Ref findit#29