Fixed issue with MGXS merging - now null out base tallies since fluxes cannot be merged and reused to compute merged cross sections
Fixed issue with MGXS merging - now null out base tallies since fluxes cannot be merged and reused to compute merged cross sections

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