Fix bug in i18n/l10n optimization

This fixes a off-by-one buffer overrun bug introduced in
2017-06-04T15:39:37Z!eggert@cs.ucla.edu.  Problem uncovered by an
experimental version of Emacs built with -fcheck-pointer-bounds
and running on Intel MPX hardware.
* src/editfns.c (styled_format): Avoid overrunning internal buffers.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/editfns.c b/src/editfns.c
index f275f33fc52..f7c26b900a0 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -4919,7 +4919,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                   else if (discarded[bytepos] == 1)
                     {
                       position++;
-                      if (translated == info[fieldn].start)
+                      if (fieldn < nspec && translated == info[fieldn].start)
                         {
                           translated += info[fieldn].end - info[fieldn].start;
                           fieldn++;
@@ -4939,7 +4939,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                   else if (discarded[bytepos] == 1)
                     {
                       position++;
-                      if (translated == info[fieldn].start)
+                      if (fieldn < nspec && translated == info[fieldn].start)
                         {
                           translated += info[fieldn].end - info[fieldn].start;
                           fieldn++;