Added fix for the prompt-injector so it doesn't console error on sites without source.top

Author: David Haeffner

packages/selenium-ide/src/content/prompt-injector.js

@@ -47,6 +47,7 @@ export function detach() {
 
 function handleMessage(event, selenium) {
   if (
+    event.source &&
     event.source.top == window &&
     event.data &&
     event.data.direction == 'from-page-script'