[sfnt] Fix postscript name for default instance of variation fonts.

Problem reported by Behdad.

* src/sfnt/sfdriver.c (sfnt_get_ps_name): Test
`is_default_instance'.

ChangeLog

@@ -1,3 +1,12 @@
+2017-09-21  Werner Lemberg  <wl@gnu.org>
+
+	[sfnt] Fix postscript name for default instance of variation fonts.
+
+	Problem reported by Behdad.
+
+	* src/sfnt/sfdriver.c (sfnt_get_ps_name): Test
+	`is_default_instance'.
+
 2017-09-21  Werner Lemberg  <wl@gnu.org>
 
 	[truetype] Fix `mmvar' array pointers, part 2.

src/sfnt/sfdriver.c

@@ -1029,7 +1029,7 @@
       return face->postscript_name;
 
 #ifdef TT_CONFIG_OPTION_GX_VAR_SUPPORT
-    if ( face->blend )
+    if ( face->blend && !face->is_default_instance )
     {
       face->postscript_name = sfnt_get_var_ps_name( face );
       return face->postscript_name;