[aat] Fix LookupFormat10 sanitize

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11060
diff --git a/src/hb-aat-layout-common.hh b/src/hb-aat-layout-common.hh
index 60724c1..a99ccaf 100644
--- a/src/hb-aat-layout-common.hh
+++ b/src/hb-aat-layout-common.hh
@@ -285,7 +285,7 @@
 		valueArrayZ;	/* The lookup values (indexed by the glyph index
 				 * minus the value of firstGlyph). */
   public:
-  DEFINE_SIZE_ARRAY (6, valueArrayZ);
+  DEFINE_SIZE_ARRAY (8, valueArrayZ);
 };
 
 template <typename T>