[truetype] Fix MVAR post-action handling.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=509

* src/truetype/ttobjs.c (tt_size_reset): Do nothing for CFF2.  This
is important to make `tt_size_reset_iterator' (called in
`tt_apply_mvar') always work.

ChangeLog

@@ -1,3 +1,15 @@
+2017-02-02  Werner Lemberg  <wl@gnu.org>
+
+	[truetype] Fix MVAR post-action handling.
+
+	Reported as
+
+	  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=509
+
+	* src/truetype/ttobjs.c (tt_size_reset): Do nothing for CFF2.  This
+	is important to make `tt_size_reset_iterator' (called in
+	`tt_apply_mvar') always work.
+
 2017-02-02  Werner Lemberg  <wl@gnu.org>
 
 	Make compilation with FT_CONFIG_OPTION_PIC work again.

src/truetype/ttobjs.c

@@ -1212,10 +1212,14 @@
     FT_Size_Metrics*  metrics;
 
 
-    size->ttmetrics.valid = FALSE;
-
     face = (TT_Face)size->root.face;
 
+    /* nothing to do for CFF2 */
+    if ( face->isCFF2 )
+      return FT_Err_Ok;
+
+    size->ttmetrics.valid = FALSE;
+
     metrics = &size->metrics;
 
     /* copy the result from base layer */