[FIX] web_editor: odoo.define can be undefined if not in edit mode

Commit 933949085d added the odoo variable
definition in the iframe template so the condition which checked if
odoo.define is available had to be adapted.

addons/web_editor/views/iframe.xml

@@ -45,7 +45,7 @@
                         }
                     };
                 }
-                if(window['odoo']) {
+                if(window.odoo.define) {
                     odoo.define('web.csrf', function (require) {
                         var token = "<t t-esc="request.csrf_token(None)"/>";
                         var core = require('web.core');