fix uninitialized payload property

[ro0NL]

we use dispatch() for manual acking

i assume it's a proper client usage, since it fully handles response processing

i noticed for empty ack responses we get

In Client.php line 346:
                                                                                              
  [Error]                                                                                     
  Typed property Basis\Nats\Message\Msg::$payload must not be accessed before initialization  
                                                                                              

Exception trace:
  at /app/vendor/basis-company/nats/src/Client.php:346
 Basis\Nats\Client->onMessage() at /app/vendor/basis-company/nats/src/Client.php:325
 Basis\Nats\Client->process() at /app/vendor/basis-company/nats/src/Client.php:177
 Basis\Nats\Client->request() at /app/vendor/basis-company/nats/src/Client.php:129

this solves it

cc @nekufa :)

[ro0NL]

actually no, publish is sufficient for manual acking