[wpinet] uv: Stop creating handles when closing loop (#5102)

This prevents EventLoopRunner::Stop() from hanging in the case when
new handles are created after the async walk closes all the handles.

wpinet/src/main/native/cpp/EventLoopRunner.cpp

@@ -59,6 +59,7 @@ void EventLoopRunner::Stop() {
       h.SetLoopClosing(true);
       h.Close();
     });
+    loop.SetClosing();
   });
   m_owner.Join();
 }