[autofit] Fix HarfBuzz calling.

* src/autofit/afadjust.c (af_reverse_character_map_new)
  [FT_CONFIG_OPTION_USE_HARFBUZZ]: Use `ft_hb_enabled`.

Fixes issue #1354.
diff --git a/src/autofit/afadjust.c b/src/autofit/afadjust.c
index f55317b..6637cac 100644
--- a/src/autofit/afadjust.c
+++ b/src/autofit/afadjust.c
@@ -1355,6 +1355,7 @@
 
 #ifdef FT_CONFIG_OPTION_USE_HARFBUZZ
 
+    if ( ft_hb_enabled( globals ) )
     {
       hb_font_t  *hb_font;
       hb_face_t  *hb_face;