Using DebugInterface from ReplayObserver

I was tring to use the DebugInterface to present information within the StarCraft window. I tried the following code inside OnStep():

```
auto d = Debug();
d->DebugTextOut("blub", { 0.5f, 0.5f });
d->SendDebug();
```

During runtime, I get the following error:

> While waiting for ResponseDebug received an error.
> Error: Can't save a replay of a replay

What is the problem?
Is it a bug, then please fit it.
Is the DebugInterface not meant for ReplayObservers, then please move Debug() from Client to Agent.