Don't initialize end in pp_reverse when begin is NULL

This change is a complement to 572558b47236782e60e41bd235c96eae7cbca3db.

Arithmetic on null pointers isn't defined by the C standard, so it may crash even before entering the loop.

1 files changed, 8 insertions, 5 deletions

diff --git a/pp.c b/pp.c
index daa63af9a4..e4660b31f2 100644
--- a/pp.c
+++ b/pp.c
@@ -5418,12 +5418,15 @@ PP(pp_reverse)
 	    }
 	    else {
 		SV **begin = AvARRAY(av);
-		SV **end   = begin + AvFILLp(av);
 
-		while (begin && begin < end) {
-		    register SV * const tmp = *begin;
-		    *begin++ = *end;
-		    *end--   = tmp;
+		if (begin) {
+		    SV **end   = begin + AvFILLp(av);
+
+		    while (begin < end) {
+			register SV * const tmp = *begin;
+			*begin++ = *end;
+			*end--   = tmp;
+		    }
 		}
 	    }
 	}