build: fix rx test on undertow

- a response handler was missing

Author: jknack

modules/jooby-rxjava3/src/main/java/io/jooby/rxjava3/Reactivex.java

@@ -20,6 +20,7 @@
 import io.reactivex.rxjava3.core.Maybe;
 import io.reactivex.rxjava3.core.Observable;
 import io.reactivex.rxjava3.core.Single;
+import io.reactivex.rxjava3.disposables.Disposable;
 
 /**
  * Rx reactive filter.
@@ -53,6 +54,9 @@ public Route.Handler apply(@NonNull Route.Handler next) {
               maybe.subscribe(new RxSubscriber(ctx));
               // Return context to mark as handled
               return ctx;
+            } else if (result instanceof Disposable) {
+              // Return context to mark as handled
+              return ctx;
             }
             return result;
           };