LibWeb: Default initialize strings in MessageEventInit

Author: https://github.com/Lubrsi
Commit: 464cc55b16
Pull-request: https://github.com/SerenityOS/serenity/pull/21823
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/shannonbooth
Reviewed-by: https://github.com/trflynn89

Userland/Libraries/LibWeb/HTML/MessageEvent.h

@@ -17,8 +17,8 @@ using MessageEventSource = Variant<JS::Handle<WindowProxy>, JS::Handle<MessagePo
 
 struct MessageEventInit : public DOM::EventInit {
     JS::Value data { JS::js_null() };
-    String origin;
-    String last_event_id;
+    String origin {};
+    String last_event_id {};
     Optional<MessageEventSource> source;
 };