the server does not send back empty reply message

[mw66]

Hi,

This is related to the previous issue:

https://github.com/huntlabs/grpc-dlang/issues/33

If the user set reply message to empty, the server won't send back that message, then the application client side will wait for that empty reply forever.

A request / a reply's body is empty or not is an application logic thing, the grpc library should not check for that and decide if the request need to be handled or reply sent back, the server should always do that.