Fix broken close button in edit checks dialog

Bug: Issue 12640
Change-Id: If3a01c63b6f93ecb9e20b704b783545724525ca1
diff --git a/gr-checks/gr-checkers-list.js b/gr-checks/gr-checkers-list.js
index b7441e9..da61b22 100644
--- a/gr-checks/gr-checkers-list.js
+++ b/gr-checks/gr-checkers-list.js
@@ -200,7 +200,7 @@
   }
 
   _handleEditCancel(e) {
-    if (e.detail.reload) {
+    if (e.detail && e.detail.reload) {
       this._getCheckers();
     }
     this.$.editOverlay.close();