fixed a defect associated with Nemission<=0 case

Author: qianglbl

src/Contrl/AccSimulator.f90

@@ -1445,7 +1445,7 @@ subroutine run_AccSimulator()
           else
              flagpos = 1
           endif
-          if(grange(5).gt.0.0d0) then
+          if(grange(5).gt.0.0d0 .or. Nemission.le.0) then
              flagcathode = 0
           else
              flagcathode = 1