FIX catch warning division by 0 in `quickflat.utils.make_flatmap_image` when `nanmean=True` (#404)
FIX catch warning division by 0 in `quickflat.utils.make_flatmap_image` when `nanmean=True` (#404)

* FIX division by 0 in nanmean

* FIX ignore RuntimeWarning h/t TomDLT
gallantlab/pycortex,gallantlab/pycortex,gallantlab/pycortex,gallantlab/pycortex,gallantlab/pycortex