Stop substr($utf8) from calling get-magic twice

By calling get-magic twice, it could cause its string buffer to be
reallocated, resulting in incorrect and random return values.

1 files changed, 1 insertions, 1 deletions

diff --git a/pp.c b/pp.c
index 0c148baf2b..05a9edf482 100644
--- a/pp.c
+++ b/pp.c
@@ -3020,7 +3020,7 @@ PP(pp_substr)
     }
     tmps = SvPV_const(sv, curlen);
     if (DO_UTF8(sv)) {
-        utf8_curlen = sv_len_utf8(sv);
+        utf8_curlen = sv_len_utf8_nomg(sv);
 	if (utf8_curlen == curlen)
 	    utf8_curlen = 0;
 	else