ComputeNbody sample - compute.uniform_buffer looks not properly synchronized, it's updated right after QueueSubmit.

Please look at ComputeNBody::render and ComputeNBody::draw.
We add an WaitForIdle in Api::VulkanSample::submit_frame(), so:
For graphics sequence, it's QueueSubmit -> WaitForIdle -> graphics.uniform_buffer.update. Most samples implement similar to this.
For compute sequence, it's QueueSubmit -> compute.uniform_buffer.update, there's no synchronization between the submission and buffer-update, which I think is wrong.