Fix assert fail when fetching pos clobbers ref with undef

pos($x) returns a special magical scalar that sets the match position
on $x.  Calling pos($x) twice will provide two such scalars.  If we
set one of them to a reference, set the other to undef, and then read
the first, all hail breaks loose, because of the use of SvOK_off.

SvOK_off is not sufficient if arbitrary values can be assigned by Perl
code.  Globs, refs and regexps (among others) need special handling,
which sv_setsv knows how to do.

1 files changed, 1 insertions, 1 deletions

diff --git a/mg.c b/mg.c
index ea912b3412..604fe6bb05 100644
--- a/mg.c
+++ b/mg.c
@@ -2105,7 +2105,7 @@ Perl_magic_getpos(pTHX_ SV *sv, MAGIC *mg)
 	    sv_setuv(sv, i);
 	    return 0;
     }
-    SvOK_off(sv);
+    sv_setsv(sv,NULL);
     return 0;
 }