Destroy abandoned websocket ops on shutdown

fix #1358

include/boost/beast/websocket/impl/stream_impl.hpp

@@ -138,6 +138,18 @@ struct stream<NextLayer, deflateSupported>::impl_type
         timeout_opt.keep_alive_pings = false;
     }
 
+    void
+    shutdown() override
+    {
+        op_rd.reset();
+        op_wr.reset();
+        op_ping.reset();
+        op_idle_ping.reset();
+        op_close.reset();
+        op_r_rd.reset();
+        op_r_close.reset();
+    }
+
     void
     open(role_type role_)
     {