Fix graphite intergration reordered clusters problem

src/hb-graphite2.cc

diff --git a/src/hb-graphite2.cc b/src/hb-graphite2.cc
index 6f0598d..531c2ad 100644
--- a/src/hb-graphite2.cc
+++ b/src/hb-graphite2.cc
@@ -307,6 +307,8 @@
     curradv = gr_slot_origin_X(gr_seg_first_slot(seg));
     clusters[0].advance = gr_seg_advance_X(seg) - curradv;
   }
+  else
+    clusters[0].advance = 0;
   for (is = gr_seg_first_slot (seg), ic = 0; is; is = gr_slot_next_in_segment (is), ic++)
   {
     unsigned int before = gr_slot_before (is);
@@ -332,7 +334,10 @@
       if (HB_DIRECTION_IS_BACKWARD(buffer->props.direction))
         c->advance = curradv - gr_slot_origin_X(is);
       else
-        clusters[ci].advance = gr_slot_origin_X(is) - curradv;
+      {
+        c->advance = 0;
+        clusters[ci].advance += gr_slot_origin_X(is) - curradv;
+      }
       ci++;
       curradv = gr_slot_origin_X(is);
     }
@@ -345,7 +350,7 @@
   if (HB_DIRECTION_IS_BACKWARD(buffer->props.direction))
     clusters[ci].advance += curradv;
   else
-    clusters[ci].advance = gr_seg_advance_X(seg) - curradv;
+    clusters[ci].advance += gr_seg_advance_X(seg) - curradv;
   ci++;
 
   for (unsigned int i = 0; i < ci; ++i)