Bug 1601067 - Only send ActionDelegate:Attached when the delegate is not null. r=snorp

We use this to send a default action to the embedder, but if no one is
listening there's no point, and it causes problems in tests because sometimes
the delegate is attached / reattached too quickly and the second delegate will
end up getting two messages by mistake.

Differential Revision: https://phabricator.services.mozilla.com/D72974

mobile/android/geckoview/src/main/java/org/mozilla/geckoview/WebExtension.java

@@ -1578,8 +1578,10 @@ public class WebExtension {
         final GeckoBundle bundle = new GeckoBundle(1);
         bundle.putString("extensionId", id);
 
-        EventDispatcher.getInstance().dispatch(
+        if (delegate != null) {
-                "GeckoView:ActionDelegate:Attached", bundle);
+            EventDispatcher.getInstance().dispatch(
+                    "GeckoView:ActionDelegate:Attached", bundle);
+        }
     }
 
     /** Describes the signed status for a {@link WebExtension}.