Refactor an each/else to an if/each/else to work around an Ember bug
Refactor an each/else to an if/each/else to work around an Ember bug

See https://github.com/emberjs/ember.js/issues/12716

This problem occurs when using a 'collapsable' table.
When a row group is initially rendered in the collapsed state it `yield`s; any {{table-columns}} used inside here aren't cleaned up properly (they're removed from the DOM but `willDestroyElement` is never called so they never unregister, and the corresponding header will always hold a reference to this outdated component.)

cball/justa-table,cball/justa-table