Fix harfbuzz read past end of string on arabic text.

third_party/harfbuzz/src/harfbuzz-arabic.c

 /*
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * This is part of HarfBuzz, an OpenType Layout engine library.
  *
  * Permission is hereby granted, without written agreement and without
  * license or royalty fees, to use, copy, modify, and distribute this
  * software and its documentation for any purpose, provided that the
  * above copyright notice and the following two paragraphs appear in
  * all copies of this software.
@@ skipping 991 matching lines @@
     uc = item->string + item->item.pos;
 
     properties = props;
     f = 0;
     l = item->item.length;
     if (item->item.pos > 0) {
         --f;
         ++l;
         ++properties;
     }
-    if (f + l < item->stringLength) {
+    if (f + l + item->item.pos < item->stringLength) {
         ++l;
     }
     getArabicProperties(uc+f, l, props);
 
     for (i = 0; i < (int)item->num_glyphs; i++) {
         apply[i] = 0;
 
         if (properties[i].shape == XIsolated)
             apply[i] |= MediProperty|FinaProperty|InitProperty;
         else if (properties[i].shape == XMedial)
@@ skipping 56 matching lines @@
                                       item->item.bidiLevel % 2);
 
     HB_FREE_STACKARRAY(shapedChars);
 
     if (!haveGlyphs)
         return FALSE;
 
     HB_HeuristicPosition(item);
     return TRUE;
 }
-
-