Fix #17375 (rcatline didn't work on a formerly-defined undef) by

checking for SvOK in do_readline().

p4raw-id: //depot/perl@17910

1 files changed, 7 insertions, 3 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 2895069755..f0d3e98845 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -1484,10 +1484,14 @@ Perl_do_readline(pTHX)
 	tmplen = SvLEN(sv);	/* remember if already alloced */
 	if (!tmplen)
 	    Sv_Grow(sv, 80);	/* try short-buffering it */
-	if (type == OP_RCATLINE)
+	offset = 0;
+	if (type == OP_RCATLINE && SvOK(sv)) {
+	    if (!SvPOK(sv)) {
+		STRLEN n_a;
+		(void)SvPV_force(sv, n_a);
+	    }
 	    offset = SvCUR(sv);
-	else
-	    offset = 0;
+	}
     }
     else {
 	sv = sv_2mortal(NEWSV(57, 80));