Clear error codes idiomatically

example/http/client/async-ssl/http_client_async_ssl.cpp

@@ -191,7 +191,7 @@ public:
         {
             // Rationale:
             // http://stackoverflow.com/questions/25587403/boost-asio-ssl-async-shutdown-always-finishes-with-an-error
-            ec.assign(0, ec.category());
+            ec = {};
         }
         if(ec)
             return fail(ec, "shutdown");