BUG: Protect kahan_sum from empty arrays
BUG: Protect kahan_sum from empty arrays

Return a default value when passed an empty array

charris/numpy,anntzer/numpy,jakirkham/numpy,mattip/numpy,mhvk/numpy,numpy/numpy,seberg/numpy,rgommers/numpy,mhvk/numpy,numpy/numpy,pdebuyl/numpy,pdebuyl/numpy,endolith/numpy,seberg/numpy,mattip/numpy,endolith/numpy,rgommers/numpy,charris/numpy,jakirkham/numpy,anntzer/numpy,mhvk/numpy,jakirkham/numpy,jakirkham/numpy,endolith/numpy,endolith/numpy,jakirkham/numpy,pdebuyl/numpy,rgommers/numpy,mattip/numpy,anntzer/numpy,charris/numpy,numpy/numpy,mattip/numpy,mhvk/numpy,seberg/numpy,charris/numpy,mhvk/numpy,anntzer/numpy,rgommers/numpy,numpy/numpy,pdebuyl/numpy,seberg/numpy