[hb-old] Fix Arabic cursive positioning

Backporting from upstream:

commit b847f24ce855d24f6822bcd9c0006905e81b94d8
Author: Behdad Esfahbod <behdad@behdad.org>
Date:   Wed Jul 25 19:29:16 2012 -0400

    [arabic] Fix Arabic cursive positioning

    This was clearly broken in testing.  Who knows...  Fixes for me.
    Test with a Nastaleeq font, or with Arabic Typesetting.

    Backporting from Chromium.

src/hb-old/harfbuzz-shaper.cpp

@@ -923,7 +923,7 @@ HB_Bool HB_OpenTypePosition(HB_ShaperItem *item, int availableGlyphs, HB_Bool do
                 adjustment = HB_FIXED_ROUND(adjustment);
 
             if (positions[i].new_advance) {
-                advances[i] = adjustment;
+                ; //advances[i] = adjustment;
             } else {
                 advances[i] += adjustment;
             }