[perl #119949] Stop undef *_, goto &sub from crashing

Commit 049bd5ffd62b fixed problems with the wrong @_ being visible
after *_ modification followed by goto.  In so doing, it made it
possible for a null to be placed at the start of the target sub’s
pad, because it was not checking that the array it got from PL_defgv
was actually non-null.  Simply adding the check makes everything work.

1 files changed, 4 insertions, 2 deletions

diff --git a/pp_ctl.c b/pp_ctl.c
index 2b7b3a9fb4..d0a56bab84 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -2932,8 +2932,10 @@ PP(pp_goto) /* also pp_dump */
 		       to freed memory as the result of undef *_.  So put
 		       it in the callee’s pad, donating our refer-
 		       ence count. */
-		    SvREFCNT_dec(PAD_SVl(0));
-		    PAD_SVl(0) = (SV *)(cx->blk_sub.argarray = arg);
+		    if (arg) {
+			SvREFCNT_dec(PAD_SVl(0));
+			PAD_SVl(0) = (SV *)(cx->blk_sub.argarray = arg);
+		    }
 
 		    /* GvAV(PL_defgv) might have been modified on scope
 		       exit, so restore it. */