FIX: calendar_details could be undefined at this point

FIX: calendar_details could be undefined at this point

diff --git a/assets/javascripts/initializers/discourse-calendar.js.es6 b/assets/javascripts/initializers/discourse-calendar.js.es6
index 541b4fc..54c56ab 100644
--- a/assets/javascripts/initializers/discourse-calendar.js.es6
+++ b/assets/javascripts/initializers/discourse-calendar.js.es6
@@ -198,7 +198,7 @@ function initializeDiscourseCalendar(api) {
   }
 
   function _setDynamicCalendarEvents(calendar, post) {
-    post.calendar_details.forEach(detail => {
+    (post.calendar_details || []).forEach(detail => {
       let event = _buildEventObject(
         detail.from
           ? {

GitHub sha: 9a1e5a4e