Return 0.0 from MGXS.get_nuclide_density if nuclide not in list
Return 0.0 from MGXS.get_nuclide_density if nuclide not in list

johnnyliu27/openmc,samuelshaner/openmc,liangjg/openmc,bhermanmit/openmc,wbinventor/openmc,liangjg/openmc,bhermanmit/openmc,smharper/openmc,samuelshaner/openmc,amandalund/openmc,paulromano/openmc,mit-crpg/openmc,mit-crpg/openmc,shikhar413/openmc,amandalund/openmc,smharper/openmc,shikhar413/openmc,walshjon/openmc,johnnyliu27/openmc,wbinventor/openmc,liangjg/openmc,smharper/openmc,samuelshaner/openmc,johnnyliu27/openmc,mit-crpg/openmc,mit-crpg/openmc,wbinventor/openmc,walshjon/openmc,amandalund/openmc,walshjon/openmc,shikhar413/openmc,johnnyliu27/openmc,amandalund/openmc,liangjg/openmc,samuelshaner/openmc,paulromano/openmc,walshjon/openmc,wbinventor/openmc,paulromano/openmc,paulromano/openmc,smharper/openmc,shikhar413/openmc