FIX: More robust `afterRender` for the composer

app/assets/javascripts/discourse/components/composer-body.js.es6

@@ -30,17 +30,17 @@ export default Ember.Component.extend({
   @observes('composeState', 'composer.action')
   resize() {
     Ember.run.scheduleOnce('afterRender', () => {
+      if (!this.element || this.isDestroying || this.isDestroyed) { return; }
+
       const h = $('#reply-control').height() || 0;
       this.movePanels(h + "px");
 
       // Figure out the size of the fields
       const $fields = this.$('.composer-fields');
-        if ($fields) {
       const fieldPos = $fields.position();
       if (fieldPos) {
         this.$('.wmd-controls').css('top', $fields.height() + fieldPos.top + 5);
       }
-        }
 
       // get the submit panel height
       const submitPos = this.$('.submit-panel').position();