Fixed outside lattice material bug for #313
Fixed outside lattice material bug for #313

lat % outside corresponds to the outside material id.  The proper number to use
is c % material which references the actual material index.

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