fix bug in initializing the starting point for meshline plotting
fix bug in initializing the starting point for meshline plotting

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