Reading a fits file returns empty(?) dask array

Here I'm trying to open a fits file with astropy.io.fits:
```
In[42]: f=fits.open('20161214_00034.fits')
In[43]: f[1].data.shape
Out[43]: (5776,)
```
This is correct. However when reading with FITSArraySource, I get some warnings and the resulting dask array is empty
```
In[44]: f=FITSArraySource('20161214_00034.fits')
In[45]: f.shape
WARNING: FITSFixedWarning: The WCS transformation has more axes (2) than the image it is associated with (0) [astropy.wcs.wcs]
WARNING: FITSFixedWarning: 'datfix' made the change 'Set DATE-REF to '1858-11-17' from MJD-REF'. [astropy.wcs.wcs]
In[46]: f.to_dask().shape
Out[46]: ()
In[47]:
```