Fix material filter bug
Fix material filter bug

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