r638: - Fix perl warning with "isr stat" if there is no memory image (i.e., the guest has been shut down)
r638: - Fix perl warning with "isr stat" if there is no memory image (i.e., the
guest has been shut down)

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr