Native resampler fails with 3D DataArrays

[djhoese]

Describe the bug
The native resampler fails to resample (replicate) any RGB or other DataArray with more than two dimensions. I think I have a solution, but need to test. Making this issue in case this turns out to be more annoying than I think it is.

To Reproduce

scn = Scene(reader='abi_l1b', filenames=[...])
scn.load(['airmass', 'natural_color'])
new_scn = scn.resample(resampler='native')

Expected behavior
No exception.

Actual results

  File "/Users/davidh/repos/git/satpy/satpy/resample.py", line 264, in resample
    return self.compute(data, cache_id=cache_id, **kwargs)
  File "/Users/davidh/repos/git/satpy/satpy/resample.py", line 778, in compute
    repeats[data.dims.index('bands')]
KeyError: 0