[BUG]The rest request was sent before the handler was ready

[ztkmkoo]

According to #87, If sending lots request, it seems netty push the io event to io.github.ztkmkoo.dss.core.network.rest.handler.DssRestHandler before the ActorContext<DssRestChannelHandlerCommand> is ready.

If context is null, send back 500 error response to client. (i think..)

If you have a better way, please give me some advices.

[ztkmkoo]

@ParkSale