Fix invokable order of invocation:

The call to the final handler in a composed operation MUST be
the last thing performed, as the handler may cause the end of
object lifetimes before it returns.

include/beast/websocket/impl/write_frame_op.ipp

@@ -256,8 +256,8 @@ operator()(
             deallocate(d.tmp, d.tmp_size, d.h);
         d.tmp = nullptr;
     }
-    d.h(ec);
     d.ws.rd_op_.maybe_invoke();
+    d.h(ec);
 }
 
 } // websocket