Support toggle+widget buttons in plugin-framework

Change-Id: Ibf2b80efc1eeda2f51dedf4a7f3cd5ac67325ef9
diff --git a/dev/js/src/plugin/service.js b/dev/js/src/plugin/service.js
index ef6836c..7b4e998 100644
--- a/dev/js/src/plugin/service.js
+++ b/dev/js/src/plugin/service.js
@@ -107,10 +107,12 @@
      */
     sendMsg : function (d) {
       let iframe = this.load();
-      iframe.contentWindow.postMessage(
-        d,
-        '*'
-      ); // TODO: Fix origin
+      if (iframe && iframe.contentWindow) {
+        iframe.contentWindow.postMessage(
+          d,
+          '*'
+        ); // TODO: Fix origin
+      };
     },
 
     // onClose : function () {},