Fix bug re: first nuclide with zero density
Fix bug re: first nuclide with zero density

amandalund/openmc,mit-crpg/openmc,mit-crpg/openmc,mit-crpg/openmc,paulromano/openmc,amandalund/openmc,paulromano/openmc,walshjon/openmc,paulromano/openmc,liangjg/openmc,smharper/openmc,walshjon/openmc,walshjon/openmc,mit-crpg/openmc,smharper/openmc,shikhar413/openmc,smharper/openmc,paulromano/openmc,liangjg/openmc,shikhar413/openmc,smharper/openmc,shikhar413/openmc,amandalund/openmc,liangjg/openmc,walshjon/openmc,liangjg/openmc,amandalund/openmc,shikhar413/openmc