In other words, on the current master, if I do this from the `sample` directory in the sample dataset:
```
mne_average_forward_solutions --fwd sample_audvis-meg-oct-6-fwd.fif --fwd sample_audvis-meg-oct-6-fwd.fif --out test-fwd.fif
```
And then try to load `test-fwd.fif`, we get this:
```
>>> fwd = mne.read_forward_solution('test-fwd.fif')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "mne/utils.py", line 278, in dec
    return function(*args, **kwargs)
  File "mne/forward.py", line 278, in read_forward_solution
    raise ValueError('Could not read the source spaces (%s)' % inst)
ValueError: Could not read the source spaces (Last value of index pointer should be less than the size of index and data arrays)
```
So we'll have to figure that one out at some point... notably I can read other averaged forward solutions I've made, so I'm not sure what's up with this one.