fixed bug in tally.get_slice() method for mesh filters
fixed bug in tally.get_slice() method for mesh filters

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