[repacker] correct MarkArray size calculation.

src/graph/markbasepos-graph.hh

diff --git a/src/graph/markbasepos-graph.hh b/src/graph/markbasepos-graph.hh
index 86ed3ca..390bc72 100644
--- a/src/graph/markbasepos-graph.hh
+++ b/src/graph/markbasepos-graph.hh
@@ -150,7 +150,8 @@
     }
 
     this->len = new_index;
-    o.tail = o.head + MarkArray::min_size + OT::Offset16::static_size * new_index;
+    o.tail = o.head + MarkArray::min_size +
+             OT::Layout::GPOS_impl::MarkRecord::static_size * new_index;
     return true;
   }