nthcdr: terminate loop if end of list hit.

* lib.c (nthcdr): Terminate loop when nil is
hit rather than continuing to count down to zero.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib.c b/lib.c
index 31351fba..f70372fb 100644
--- a/lib.c
+++ b/lib.c
@@ -726,7 +726,7 @@ val nthcdr(val pos, val list)
 
   gc_hint(list);
 
-  while (n-- > 0)
+  while (list && n-- > 0)
     list = cdr(list);
 
   return list;