Fix nullptr crash

src/cpp/client/client_unary_call.cc

@@ -64,8 +64,10 @@ Status BlockingUnaryCall(ChannelInterface *channel, const RpcMethod &method,
 
 class ClientAsyncRequest final : public CallOpBuffer {
  public:
+  bool got_message = false;
   void FinalizeResult(void** tag, bool* status) override {
     CallOpBuffer::FinalizeResult(tag, status);
+    *status &= got_message;
     delete this;
   }
 };
@@ -81,7 +83,7 @@ void AsyncUnaryCall(ChannelInterface *channel, const RpcMethod &method,
   buf->AddSendInitialMetadata(context);
   buf->AddSendMessage(request);
   buf->AddRecvInitialMetadata(&context->recv_initial_metadata_);
-  buf->AddRecvMessage(result, nullptr);
+  buf->AddRecvMessage(result, &buf->got_message);
   buf->AddClientSendClose();
   buf->AddClientRecvStatus(&context->trailing_metadata_, status);
   call.PerformOps(buf);