Bail out of _updateOptionsAndResults if `isDestroying` (#1023)
Bail out of _updateOptionsAndResults if `isDestroying` (#1023)

I opened a similar PR while back, but declined when I couldn't consistently reproduce the issue. Now I can, although the setup is hard to explain. The specific error I get is `TypeError: Cannot read property 'isOpen' of undefined`, which happens on line 540 (`publicAPI.isOpen`).

I have a page with two ember-power-selects. When the first is selected, it populates the choices of the second (from a `hasMany` association from the selected model). When ember tears down all the models at the end of an acceptance test, it triggers the change event on the `hasMany` relationship, causing ember-power-select to want to update, but since everything is mid-teardown I get the error I mentioned. There's a lot of other stuff going on in my test, but I think it boils down to a race condition that this PR fixes.
esbanarango/ember-power-select,cibernox/ember-power-select,cibernox/ember-power-select,esbanarango/ember-power-select,cibernox/ember-power-select,esbanarango/ember-power-select,cibernox/ember-power-select