FIX: Check whether edit_mod.app actually exists

src/core/js/ext_editmode_wysiwyg_text.js

@@ -82,7 +82,7 @@ var ext_editmode_wysiwyg_text = function ($, logger, ClassicEditor, edit_mode, g
     }
 
     var init = function () {
-        if (edit_mode.app.entity) {
+        if (edit_mode.app && edit_mode.app.entity) {
             // replace text areas if we're already in the edit mode and all
             // events did fire already.
             replaceTextAreas(edit_mode.app.entity);