No clear error message, when writing comment in config definition line

```
import sacred
ex = sacred.Experiment('test')


@ex.config
def config():   # some comment
    a = 1


@ex.automain
def main(a):
    print(a + 1)
```
The above code example create an AssertionError in the following sacred file:

> sacred/config/config_scope.py", line 102, in get_function_body

without any further information.
Is this desired behavior?
