Fix temperature indexing error for plot_xs
Fix temperature indexing error for plot_xs

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