setpgrp() should extend the stack before modifying it

As reported by Marcin Owsiany in <http://bugs.debian.org/512796>,
invoking setpgrp without any arguments could corrupt the stack.

1 files changed, 1 insertions, 0 deletions

diff --git a/pp_sys.c b/pp_sys.c
index cfbf9182ea..0d2c970ff1 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -4318,6 +4318,7 @@ PP(pp_setpgrp)
     if (MAXARG < 2) {
 	pgrp = 0;
 	pid = 0;
+	XPUSHi(-1);
     }
     else {
 	pgrp = POPi;