Optional argument nc can not be accessed if it is not present.

diff --git a/src/ext/lclist.f90 b/src/ext/lclist.f90
index 3940ee3..cfb0a4e 100644
--- a/src/ext/lclist.f90
+++ b/src/ext/lclist.f90
@@ -1049,15 +1049,21 @@ contains
     i3 = 0
     loop3 : do
        acc3 = .false.
-       if (present(nc) .and. i3 >= nc(3)) exit loop3
+       if (present(nc)) then
+          if(i3 >= nc(3)) exit loop3
+       end if
        i2 = 0
        loop2 : do
           acc2 = .false.
-          if (present(nc) .and. i2 >= nc(2)) exit loop2
+          if (present(nc)) then
+             if(i2 >= nc(2)) exit loop2
+          end if
           i1 = 0
           loop1 : do
              acc1 = .false.
-             if (present(nc) .and. i1 >= nc(1)) exit loop1
+             if (present(nc)) then
+                if(i1 >= nc(1)) exit loop1
+             end if

              ! don't include T = (0,0,0)
              if (all((/i1,i2,i3/) == 0)) then