FIX: Only trigger callback for parent transition events.

* This fixes a bug where multiple requests were being
  made to the server whenever the composer is opened.

app/assets/javascripts/discourse/lib/after-transition.js.es6

@@ -25,5 +25,8 @@ var transitionEnd = (function() {
 })();
 
 export default function (element, callback) {
-  return $(element).on(transitionEnd, callback);
+  return $(element).on(transitionEnd, event => {
+    if (event.target !== event.currentTarget) return;
+    return callback(event);
+  });
 }