Fix a missing as_ref that caused boxed endpoints to enter an infinite loop

I also added a test for this that shows it now works.
thanks to Hasali19 for noticing this

Author: mendelt

src/endpoint.rs

@@ -122,6 +122,6 @@ where
 #[async_trait]
 impl<State: Clone + Send + Sync + 'static> Endpoint<State> for Box<dyn Endpoint<State>> {
     async fn call(&self, request: Request<State>) -> crate::Result {
-        self.call(request).await
+        self.as_ref().call(request).await
     }
 }

tests/endpoint.rs

@@ -0,0 +1,25 @@
+use tide::http::{Method, Request, Url};
+use tide::Response;
+
+#[async_std::test]
+async fn should_accept_boxed_endpoints() {
+    fn endpoint() -> Box<dyn tide::Endpoint<()>> {
+        Box::new(|_| async { Ok("hello world") })
+    }
+
+    let mut app = tide::Server::new();
+    app.at("/").get(endpoint());
+
+    let mut response: Response = app
+        .respond(Request::new(
+            Method::Get,
+            Url::parse("http://example.com/").unwrap(),
+        ))
+        .await
+        .unwrap();
+
+    assert_eq!(
+        response.take_body().into_string().await.unwrap(),
+        "hello world"
+    );
+}