Have EventLoopClosed contain the original event (#1294)

* Fix issue #1292

* Remove "optionally" from changelog entry

src/platform_impl/web/event_loop/proxy.rs

@@ -11,7 +11,7 @@ impl<T: 'static> Proxy<T> {
         Proxy { runner }
     }
 
-    pub fn send_event(&self, event: T) -> Result<(), EventLoopClosed> {
+    pub fn send_event(&self, event: T) -> Result<(), EventLoopClosed<T>> {
         self.runner.send_event(Event::UserEvent(event));
         Ok(())
     }