fix IPython.embed

without this change, IPython.embed throws the following traceback:

```
  File "explete.py", line 9, in dump_inputs
   IPython.embed()
 File "/home/pi/code/ipython/IPython/terminal/embed.py", line 287, in embed
   config = load_default_config()
 File "/home/pi/code/ipython/IPython/terminal/ipapp.py", line 379, in
load_default_config
   for cf in Application._load_config_files("ipython_config",
path=profile_dir):
 File "/home/pi/code/ipython/IPython/config/application.py", line 527, in
_load_config_files
   log.debug("Loaded config file: %s", loader.full_filename) AttributeError:
'NoneType' object has no attribute 'debug'
```

@Carreau was the last to poke around in this part of the code, so pinging him,
just in case