Don't swallow errors once they've been popped up

app/assets/javascripts/discourse/lib/ajax-error.js.es6

@@ -55,4 +55,8 @@ export function throwAjaxError(undoCallback) {
 
 export function popupAjaxError(error) {
   bootbox.alert(extractError(error));
+
+  error._discourse_displayed = true;
+  // We re-throw in a catch to not swallow the exception
+  throw error;
 }